Why do most Christians and Muslims like picking on Scientology?

Because it is generally believed that Scientology isn't a religion at all, but a cult. You shouldn't have to buy your way into a religion. Also the press is full of reports about members being forced to have abortions, work for a few dollars a week and doing other unlawful stuff. But also remember, the Catholics are also getting quite a beating at the moment with all the child abuse allegations etc. and the religion (Exteme branches of Islam?) which advocate honour killings. They are all copping it at the moment, not just Scientology.