Palindrome,
I think the problem lies in the fact that not many here are aware that śramaṇa, ājīvikā, etc., were non-vedic (even anti-vedic) systems of philosophical thought which were very much there in pre-buddhist India. Both Buddhism and Jainism adopted certain aspects of these miscellaneous traditions into their own and thus the word śramaṇa has come to be identified with Buddhism mainly. Your fault lies in "trying to teach veda by reciting into the ears of the quadruped known for its highly musical sound", as the adage goes
.
Ah, well, not just central asia and old world europe, but parts of what we call india also was animist, nature-worshiping, with or without primitive concepts of a supreme. Some call the old world 'pagan', some use the word 'shamanism' to indicate belief systems of the old world.
From the natural wondering of man (on existence and natural phenomenon), there arose many streams of thinking, which formed part of faith. It is not possible to account how many and what types of faith systems existed in those tribal periods. For want of a better word some use the word Shramana (pali Samana) to indicate a wide variety of beliefs of various peripatetic renunciates.
Of the religions that came to exist, Jaina religion's shramana traditions are the oldest. Am not sure how it is possible to say Shramana came to be identified with Buddhism mainly. Buddha left home, became a Shraman monk and started the Buddist shramana traditions. The Jaina shramana and Buddhist shramana have similar beliefs with respect to karma, moksha/nirvana, etc. If there is a historical context, why Shramana came to be identified with Buddhism mainly, would like to know.
Addition:
Decided to add the portion below so it is clear how vedic religion stands in comparison to jains and buddhists.
Whatever was vedic (belief system of vedic speakers), found opposition in vedas itself. Their staunch enemies, the asuras, were deviled. The brahmana texts found a great deal of opposition from those who opposed animal sacrifice.
As
already noted there was decreasing popularity of brahmana sacrifices, since mere rituals could not satisfy people (plus for a large part they were restricted to the elite yajamans). So as a reaction, aranyakas were composed to give philosophical interpretations to the brahmana sacrifices. Thereafter, the upanishads were composed.
The "thinking" attitude, plus the renunciate systems of shramanas (with their explanations of karma, samsara, etc) were incorporated into the upanishads. Due to this reason, it is argued there were renunciates in vedic society. However, this is not true. The Yatis and Munis were looked down upon; as we had
previously noted Indra threw Yatis to Hyenes. This point was preserved in the Atharva. If there was a class of sages in vedic society they were most certainly not the shramana renunciates.
Mahavira
There is confusion on Mahavira. Some books claim he was brahman, some claim he was a kshatriya (like buddha). Many books use the word 'kshatriya' as though being a warrior alone conferred the varna on them automatically; without belonging to the culture and/or without the use of appropriate ritualism. Mostly these books are from colonial period, by those who wanted to seek (as well as impose) varna terms.
The term 'brahman' in Jainism and Buddhism is debatable; as neither buddhists not jains perform brahmanical sacrifices. Jains started using varna terms in 8th century due to competition with brahmins. Jinasena began (the system of) using varna terms through jain puranas compositions.
Additionally, the term 'brahmana', in buddhism and jainism, has an entirely different context, as one who does tapas. This is opposed to the term 'brahmana' of vedic religion who performs sacrifices to vedic gods. Obviously, Mahavira was not performing fire sacrifices to vedic gods, so he could not have been from a 'brahmin' family. We do not find evidence that Mahavira or his family was following rituals of a Kshatriya either (so it is doubtful if he was from a kshatriya family).
Instead of standing up for the teachings of the tirthankaras, it sad jains fell for varna terms.
Buddha
Now comes the association of Buddha with the Angirasas. In the Pali Canon, Buddha is called an Angirasa. This
particular book argues, if Buddha was called an Angirasa in a bid for a takeover. By doing so, (as someone shining literally as Agni) Buddha is made equal to a vedic god (which would mean Buddha is no less than the gods of the vedic people).
Plus
this book (on early brahmanical gotras) says Buddha was an Ikshvaku and claimed the Adiccha gotra. By virtue of Adiccha (Aditya) gotra, it is claimed he was a Suryavanshi and Sakya Jati. As
noted here the context of gotras in Buddhism is different from the Brahmin one.
Buddha's personal name, Gautama was not his gotra (as was claimed in wiki and many sites copying wiki). If at all he had any connection with Gautama, it cud be only from his mother's side; which
this book also explains. Buddha's mother's sister (who was also his stepmother) was named Mahaprajapati Gotami, and if that indicates a gotra, then his gotra could not have been gautama, since marriage within gotra could not have taken place (meaning, his father did not marry a lady from his own gotra).
This book (by Gombrich) also says Buddha rejected brahmanical fire sacrifices because it is an antithesis of what is truly desirable. Jains also opposed those sacrifices. Little wonder then, in popular usage the term asura became applied to buddhists and jains who opposed brahmanical fire sacrifices
Today however, buddhists pay less attention to the teachings of their masters, and more attention to varna terms. Allocating varnas gained a prominent and dominant role in colonial period, due to politics of those times. Have already elaborated enough on that issue in several older posts, no point repeating here.
Final remarks
The above being so, one wonders what did Buddhism and Jainism have to do with vedic brahmanical religion. If at all anything is common to Buddhists, Jains, and those supposedly called 'hindu' today, then it is the gods of the bhakti period (and also various tantras which show up an exchange, an interaction of philosophical points. Those interested may find the book
The Roots of Tantra interesting in this regard).
The Gods of bhakti period were outside the brahmanical sacrificial religion (of vedic deities). They were sometimes associated with Shramana systems, but these became mainstream 'hindu' gods. The brahmanical religion of fire sacrifices could neither compete with the ahimsa theory, nor with the increasing popularity of non-vedic systems (which preached their philosophy in a language of the commoners for the commoners). So, for social relevance, and due to competition from non-vedic faith forms, the brahmans of that period adopted gods Shiva, Krishna, Narayana, Rama, local heroes, and local deities such as grama devas, into their fold.
Then ofcourse, there is also the claim that brahmins entered buddhist ranks and caused its downfall in the indian subcontinent. That is another story. In that regard, found
this blog view interesting.
Similar arguments are made against brahmins wrt to Mahavira --
here is a glimpse of Osho's opinion. Anyways, finally we have Shvetambara Jains who propagate the theory that Mahavira was conceived by a brahmin couple and the embryo was transferred to Trishala's womb by some magic (shows how desperate these are to somehow link mahavira to a brahmin origin). But their problem comes not from outside but from Digamber Jains who reject their story.