Have been thinking about this.
I think the credit or blame goes to the Emperor Ashoka, because he forbad the performance of the Vedic sacrifices.
This is ironic, because he is supposed to have been highly tolerant and a great example of how to build and maintain a multi-ethnic and multi-religious kingdom.
However, we may safely say that this “tolerance” is an Ashokan myth. He not only disadvantaged Vedic religion while pretending to instruct his citizens to listen to Brahmins and munis, he consistently used state taxes to found and support Buddhist institutions as well as to fund Buddhist missionary activity all the way from and Egypt to Greece and Central Asia, round to Vietnam, Cambodia, and Sri Lanka.
We may fairly say that the first attempt at world evangelisation using the instruments of state was accomplished by Buddhism, and that it was not always as peaceful as Buddhists like to think.
For example, there is evidence of Buddhist kings enforcing Buddhism by violence on native populations in Tibet and Sri Lanka.
Naturally, such kings would not have wanted their deeds to be preserved for posterity, so took care to expunge as much evidence as possible.
However, we can still see the inheritance of this attitude in the Lamaistic Buddhism of Tibet, in Cambodian, Vietnamese, Thai and Burmese Buddhism, and in Sri Lankan Buddhism which took to violence to subjugate its indigenous majority and its Tamil minority in a declared or undeclared war lasting from the 3rd century BC to 2009 (roughly 3 years ago).