Because nobody cares to actually implement the 1st Amendment seriously.
Respectfully disagree, though not for the reason ernest did.
In my view, it is not the government endorsing the Bible...it is the private individual choosing a text upon which in his own mind solemnizes the oath...so the prospect of breaking that oath should weigh more heavily in his or her mind.
See, this I can agree with. Nobody says that an elected official has to give up his or her religion. It's pretty clear that the role of the holy book is a personal one, not an official one. There are other things in our society that I'd say fall on the other side of that line, but this isn't really one.