1. The fans grew up. As you age, your musical tastes change.
2. The internet. Because of the industry, no bands can make a living. As the bands get older and have to start living the life of an adult, the realization that music does not equal a steady paycheck becomes a reality.
3. Over-saturation. Too many bands trying to do the same thing.
It is simple.
Almost exactly how I've felt for the last several years.
The big thing for me is over saturation. Way too many bands want too much attention and it all gets spread way too thin.
There was a point in time when I was literally listening to 4 or 5 new bands a day, sure they had a good song or two, but few bands these days make an entire album filled with quality songs from beginning to end like they used to, or so it seems. It got to the point where I was tired of hearing 90% of what I was hearing and scaled back to the bands I knew and loved. It might sound stupid to you, but it was wearing me out trying to "keep up" with all the new bands and keep track of them.
Anymore I stick to the ones I know won't likely disappoint: the Yellowcards, New Found Glorys, Taking Back Sundays etc. that I can listen to a whole album and enjoy and keep track of what's going on with them.
It's way too easy for bands to get their music out there and really hard for them to be "found" because of all the mediocrity out there these days, and that's sad. Not that I won't accept any new bands into my listening library, but I don't actively seek them out like I did at one point in time.