all these christian holidays USED to be christian holidays, now they are holidays that everyone celebrates except a select few. They don't celebrate it for the same reasons, but even atheists still give their kids presents on christmas, and candy (and apparently other presents that I don't get!!!) on easter. whereas with the holiday of another religion, say the afore-mentioned Ramadan for example, not everyone celebrates it. And the only people that do celebrate it are celebrating it for it's religious meaning.
I'm not saying christians don't celebrate Christmas/Easter for it's religious meanings, but other non-religious people celebrate it too. Plus Christianity still holds a majority in the US, so asking for holidays from other religions to be considered paid holidays would be like going to Judea and asking why you don't get a paid holiday for christmas. Because only a small minority will be celebrating it.