Burnout.. pure and simple (and I can say this from my own perspective too). And summer in particular is just a bad time for it IMO.
I've been in the hobby long enough now to see people come and go several times over. It is a bad time in particular with a lot of people walking away, but I think it's just a combination of factors.
And seriously, one of the hardest hits for me this year was Big Al's closing. I had no idea how dependent I had grown on them just "being there" since they were close (I worked about 5 minutes away, so it was so easy to stop in at lunchtime or on the way home from work). With them gone, and the next nearest LFS being Golds, which is a minimum 2 hour commitment for me (drive there, visit and look, drive back), I suddenly find myself not wanting to drive to the others as much either. It's funny, but yeah, Big Al's being close-by, helped me mentally to visit the other LFS's more often.
I am still at a bit of a cross-roads myself. I think I've decided to stay with my current plans but I'm still unsure for how much longer. I've found myself completely burnt out on several things, it's not just the hobby it's just a total overall thing. I sure do think that downsizing to a single tank will help me. I also find myself missing out on some of the things I used to be more involved with, that would take away from the tanks, so by downsizing in the one maybe helps open the doors to get back into those things.
And the costs. The costs of everything just keep going up and up and up. But my income stays the same. It's just making things so tight.
Something has to give.
Anyhow just my thoughts. I'm sure other people have different reasons.