Lets see perhaps the people that do this can explain to us why they do it?
A Christian does something, some crime, some attack, something. The response is that the religion was to blame, that this person did what they did BECAUSE they were a Christian.
A Muslim does something, some crime some attack, something. The response from the same people that accuse the Christian of being motivated by Religion is that this Muslim or Muslims did what they did without regards to the religion, that the religion had nothing to do with the action they took.
Perhaps it is because a Christian being blamed won't result in retaliation for the claim, but a Muslim being blamed can and does result in retaliation almost every time?
Religious prejudice manifests when someone of a given religion commits a crime, where those hostile to that religion assume all persons of that faith are likewise criminals and predisposed to committing criminal acts – it's known as a composition fallacy.
Let's look at an example of a Christian being responsible for a mass shooting, killing dozens – to other Christians the crime belongs to the shooter alone, it's assumed he's mentally ill, and even if it's determined his Christian faith played a role in the shooting, the individual is perceived to not be representative of all Christians, nor is Christianity as a faith blamed for the mass shooting.
Now, we have the same mass shooting, dozens killed, but this time a Muslim is responsible – those hostile to Islam will assume that the shooter acted on his faith alone, that all Muslims are capable of such crimes because they believe Islam is a 'terrorist religion,' and Islam as a faith should be held responsible for the mass shooting, ignoring the possibility that a Muslim can act on his own, having nothing to do with his religion.
Again, that's religious prejudice.