Well, worshipping a god because you think he's good sort of implies there are other options, which would often imply the existence of other gods. Some religions are just fine with this, and just claims theirs is the best, but Abrahamic religions seem to somewhere along the way have picked up the idea that even the existence of other gods is to be forbidden, which leads to all kinds of problems and inconsistencies with older material that doesn't believe this. It all ends up sort of neurotic.

Which incidentially is why I can't stop giggling when I think of Shinto. Shinto has "innumerable" gods, and you just pick and choose convenient ones to worship, such as those who happen to be within hearing distance, or whatever. And at some point the Buddhists show up and say, hey, you should worship the Buddha instead! And the Shintoists go, OK, he sounds pretty awesome, let's do that! And they keep worshipping their innumerable gods and also Buddha. And next, the Christians show up and say, hey, you should worship Jesus instead! And, of course, the Shintoists go, awesome, let's add him too!

I was discussing this with a Japanese friend, and the result is pretty much that as a modern Japanese person, if you're going to pray, you might very well call upon the gods in general, Buddha, and Jesus to listen to your prayer. Because hey, the more the merrier.