I think more than the attractiveness to leave the caste system in Hinduism,  a major incentive for especially these poor people is the generous packages the missionaries offer for converts. I remember going to Tatopani (?) for Bungee Jumping and there was a huge Christmas party celebrated mostly by locals who looked like recent converts. 

I don't know where I stand with regards to such activities with respect to whether the government should impose a stricter law on conversions. At least after conversion, these people are taken care of by these churches, otherwise they really had no one to take care of them, and everyone was set on exploiting them.