Why is it that I always want to do volunteer work when I'm up to my ears in other things?

Some thoughts:

1. I'm always busy, so no matter when I want to do something, I'll already be doing something else.
2. The universe has terrible timing.
3. It's a strange form of procrastination, to be productive on a project when I'm supposed to be productive on something else.
4. Once my brain is already hyper-engaged with work (or study), I'm more likely to go into overdrive and think about all sorts of things I could be doing. This probably explains the insomnia too.

I'm sure the real reasons lie somewhere in there, combined with things I haven't enumerated.