People have been so thoroughly brainwashed that they fail to notice a very important point raised by you.Multiple factors in tandem: Facing the full onslaught of Islamic invasions (Arab,Turk, Central-Asian origin), the dominant & peace-nik religion bore the brunt; particularly, their presence being more concentrated in Northern India. While the more de-centralized & geographically diffused Hindu-ism had a Renaissance of sorts, partial credit goes to the impact of Bhakti-like movements. Shaiva, Vaishnav, Shakt, Tantrik & similar traditions had deeper roots among the masses. Oh come on, I do not see any suspense here. It is mentioned all over the history text-books :thumb:
the point is that caste system, shaktism and shaivism had more appeal to indian masses than a Luxuriant vihar based meditating religion with high flown jargon on nirvana.
if one reads sangam literature one finds that tamilians from cowherders who worshipped krishna by name of kannan to farmers who worshipped indran were all hindus.
buddhism is hardly present there and whatever presence it had , that too withered away when bhakti sects made it incumbent upon elites to take note of hindu sects.
If people imagine that a farmer and a tribal from bengal will be more prone to worshipping a godless sect which is vihar centered with deep meditation rather than nature god or kali, they are beyond help.
the truth is that buddhism was never a mass religion but was a urban cult which vanished when significant chunk of patronage was withdrawn by gupta rulers.