The Destroyer album had just come out and it wasn't doing well. Neither was the single Detroit Rock City. Beth is about as far from a Kiss song as you can get, it's just drummer Peter Criss with a piano singing about how he's sad over neglecting his girlfriend for band practice again. Gene Simmons and Paul Stanley especially hated it and the only reason it was on the record at all was because the producer liked it and insisted.
It was put on the B-side because Gene and Paul thought it was such shit that it would guarantee Detroit Rock City would catch on in a big way. Instead, everyone started flipping it over and playing Beth. It ended up being their biggest hit, and gaining them lots of notice from women who weren't initially fans.
Paul and especially Gene who had no hand in writing it have always come off as super assblasted over the song and like to try and discredit Peter any way they can. Doesn't stop them from having not-Peter sing it at concerts though. And in the 80s they even had it re-recorded identically but with then-drummer Eric Carr on vocals just so that version would be played on the radio and featured in films and on albums and they didn't have to pay Peter anything. It's almost indistinguishable, and I remember reading somewhere that Carr, by all accounts an awesome guy, regretted doing that to him.
