It's Real Life, I tell you.
That's the reason why I haven't been running - and probably why a lot of the good GMs from AEGIS haven't been running games.
For me, I've found a different creative outlet in writing and may follow Dean's example - putting a lot of the elements of my imagination into games, but reserving the creme de la creme for my stories. I don't know - I'm still experimenting so I'll find out.
In the meantime, we need to encourage the next generation of GMs to start running!