Music lyrics sites used to all do this. You'd copy/paste the lyrics, and every other line was the website name or something.

Maybe because it was easy to scrape the text and make your own lyrics website or something?

I also think that google's song lyrics (on the search page itself) used to be non-selectable. But I jsut tried it, and they are selectable now.

Oh the copy paste manipulation is still not that rare. I'm speaking of sites where even if open the HTML source you only get a text garble that is magically converted into readable but uncopiable text.