Of course, the latter points to the answer to the former -- the early art was full of energy because I was full of energy while I drew it. I was passionate about comic strips and had dreams of hitting it big, at a time when hitting it big in comic strips still meant being in all the papers and having Christmas specials on TV. When I was in college, Berke Breathed was a bagjillionaire on a twenty-hour work week. These days, having a syndicated comic strip and $4.50 will buy you a latte.
Fairly early on in the SJ/NN runs I was quite aware that they were not going to make me a bagjillionaire. Even within the rapidly-contracting world of comic strips I had what's generally known as a cult audience. The readers I have love my work, and for that I'm grateful, but it seems to be a very binary thing. If my stuff doesn't ring somebody's very specific bell, they couldn't care less about it, and that's not enough to be the kind of artist who "makes it big." To do that you have to have both the core cult audience, and be something that people outside the circle are also interested enough in to follow (and spend money on). While there are some specific things I can point to (such as regularity of updates), I've never really been able to identify the qualitative difference between my work and that of "the big boys" (for lack of a better term). I know the difference is there: among other things, I find that most of their work bores me senseless. But the broader audience loves it. It's just a different mindset, I guess ... whenever I make a point to hang out with more, er, "mainstream" comic artists I feel like a stranger in a strange land.
Anyway, to be perfectly honest, it was love of the art and of my fans that kept me going for ten years, even if it was dreams of stardom that got me started. But even that couldn't keep me going forever ... art needs fuel to burn, and that fuel got used up. Most of the core themes of my work to date, I've explored about as thoroughly as I can and I don't have much to say about them any more. To keep on just saying, "ditto, ditto" would be a sure formula for stagnation. So when people send me e-mails asking why I stopped, I tell them "To avoid jumping the shark." But a more accurate reason would be to say, "Because that piece was finished. It's time to come up with a new piece."
The new piece hasn't hit me yet, but when it does, you'll know. :)