Why can I find only "Tribute Bands" for many old school, famous bands?

[Natvcali]

I have had no problem finding songs by the original artists until I decided to make a "Power Ballads" play list. All of my search results are karaoke versions, cover bands and "Tribute To's...", I've tried Def Leppard, White Snake, White Lion, Poison, Warrant, etc. I'm lucky to find one out of 50 that is the actual artist doing their own song. Is there some reason for this that I'm missing? 

[neo-x]

Some songs / artists are not available on Spotify due to copyright things I guess. When Spotify wasn't in the US of A yet, it had more songs available on the catalog. As soon as the US of A deals went down, A lot of songs etc were removed / greyed out = unplayable. Tried searching for Metallica etc.

Some info on Wikipedia says that not all great artists / bands have agreed to have their songs in Spotify catalog -> hence they are missing.

My 2 cents.