Or egotism. ;-) It's a far more common problem, I think, than mere stupidity. After all, most of the people I know are not basically stupid...but they all have a strong ego, and it is that which tends to make them exhibit prejudice toward this and that.

Then too, ignorance can add to the problem, can't it?

Funnily enough, the commercial powers that be who market songs and put them on the radio want more songs that sound almost the same as the other songs which have already sold well. Therefore they encourage imitation. If songwriters are responding to that, why be surprised?