Why would that be? The only important thing is that something is funny. The people that complain about not finding something funny or immediately have to say: /r/atheism or /r/Christianity is leaking again are the nuisance that spoils the joke.

Everyone should just swallow their pride when people are making jokes, or even try to enjoy the joke despite it being at the cost of you.

As an atheist these are one of my favourite jokes for instance:

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These jokes are at my expense, but I don't give a shit, and neither should someone else. I have seen jokes about atheism that I deem unfunny. However, because I think it is unfunny does not make it inappropriate or offensive. The only thing it being unfunny to me means is that it does not make me laugh.

People should stop drawing the line of funny/offensive where their taste of humour ends. It is highly subjective, and probably highly incompatible with the opinions of the rest of the world.

And why is religion an exception? You can also make jokes about political parties, ethnicity or other things and without a doubt that is also going to offend some or many people but like any grown-up you have to deal with that too.

So, shut it, try to enjoy it, otherwise let it pass and don't complain because it doesn't fit your style of humour.