I don't know. There are a fair few metal players on this forum, but look closely and I'm sure you'll find there are a lot of people who are into many other forms of music, guitar based or otherwise.
For example, there was a thread a few months back, which ran to a couple of pages, that was dedicated to discussion of Americana.
I think the impression you have may simply be because a lot of the metal guys post frequently, and record a fair few clips.
You are right though, BKPs seem to be very popular among metal players - I think this may be because so many of the company's humbuckers are excellent pickups for metal of one style or another.
Metal has certainly undergone something of a resurgence in popularity in recent years - nu-metal was revolted against by a new crop of traditionally-influenced, technical metal bands for whom a high degree of instrumental proficiency is a badge of honour. This might be a reason why so many 'serious' players like their metal.
Personally, I love metal in most of its forms - classic (Old Metallica/Priest/Maiden) to modern (Nevermore/Nile/Opeth). However, it's not all I listen to. I also love listening to (and playing) blues, americana, country, classic and hard rock. I also like innovative acoustic players like Tommy Emmanuel and Newton Faulkner.
Variety is fun after all. :)