It has never been the most popular of genres, hence the big risk when Lucas and TCF released Star Wars.
What then happens is every other studio piggy backs off that success until everyone realises that they dont like sci-fi that much!

The music thing about metal/rock does not hold up.
Since the early 70s, whether it be old school metal, glam, punk, emo or nu-metal, there has always been a strong prescence in the media.
Sci-Fi films as a medium has always been hit or miss, which is why a film like T2 (remember the original was only a cult hit, not a huge success) is not marketed as sci-fi, but marketed as an action movie!

Its widely aknowledged that sci-fi tends to be a cult genre.

Did Minority report or I-Robot succeed because of what they were or who was in it?

Is Transformers marketed as a sci-fi movie or is it marketed as a toy spin off?

Snarf is shit. His death will be rejoiced!