That has to do with just having a minority to blame for their countries problems. Same sort of thing happened to the gypsies. Although there were times when countries in Europe were prosperous because of Jews, like during the inquisition a lot if Spanish Jews left Spain for the Netherlands and the economy boomed there afterwards, while Spain's began to tank
I think this is because atheists are most vocal in the western world, and the dominant religions in the western world are Christianity (and Islam). that's why those two are the "targets". However yes, there are different religion out there. also, not all Christians or Muslims are bad people.
Simple, when they talk about "world" they mostly mean Western Europe & the Americas. They don't really mean the entire world, most of them are stupid like that. Don't worry, you're clearly smarter than them for knowing other religions that is different.