For me it's mostly some bugs in the more recent versions.
Silly as it may sound, having to try to find a different song when the previous choice works absolutely perfectly in the version I started building a quest in (in 2010, 1.92 b184 was still my version of choice) just... killed my will to work on ALTTS2. I don't know why -- perhaps it's because I'm almost obsessive over quest soundtracks these days? True, I could just work on it more in 1.92 (and on any machine -- DOSBox and DOS 1.92 are great to have), but when people will almost certainly play it in 2.5 anyway... yeah.
On the other hand, I can at least make other things. (The other 2.5 bugs get on my nerves, but they aren't motivation-halters.) So it's sort of... one quest freezing up. Unfortunately, the one I'd love most to complete, but... eh.
Maybe I'll finish a random thing at some point. Another issue at the moment is college classes -- when you've got one class you loathe taking away from one you were eager to participate in, it kind of makes you feel pretty perpetually crappy.