Why do Christians become Christians?

[Pat Mustard]

Buddhism got started as a rejection of the Hinduism it was spawned from.

You do realise that Buddhism is at least 100 years older than Hinduism? They both come from similar base traditions, but while Buddhism was in all likelihood a unified religion from the start (c600BCE), Hinduism was a synthesis of different traditions and religions, likely starting at around 400BCE and not finalised into anything like its current form until 500CE.