I've been thinking about why I don't use them much:
1. For editing purposes, I find it much easier to work with MIDI when it's been quantized (cut/paste etc. - Probably just laziness on my part

2. With hardware, I could just plug in and go and it seems with the software I'm always updating drivers or troubleshooting an issue that just started happening, even though it was working fine the night before.
3. I don't find many of the software synths all that interesting. Besides the fact that I need to be careful about tapping out my CPU with too much processing.
4. I'm a fairly accomplished musician (at least with the intruments I play) and I don't find the need to "correct" myself that often. Besides, I can do additional takes and sometimes they produce even more interesting results. With MIDI, I always found myself taking the easy way out, by just changing the offending note, etc.
Anyway, I also think it has a lot to do with the equipment I have. I used software a lot more when I had my BR-1600CD. When I finally killed it, I bought a Korg D3200 digital recorder and I just can't believe how easy it is to use. The computer just didn't seem interesting any more.
Thoughts? Comments?