From what I've read, Watterson simply values his privacy and his family's privacy, and he has virtually no interest in publicity for its own sake. Apparently, any former celebrity who doesn't so desperately long for attention that they appear on Dancing With the Stars or jump at every chance for an interview or public appearance is so incomprehensible to most people that the only way to make sense of it is to label them a "recluse".
I agree with you 100%, with two small exceptions.
First, it does appear that Watterson is a bit more removed from society than even your average author.
Second, I think there's a kernel of reason in the idea that someone of renown -- someone who has made a lot of money and become a familiar name in the process -- is expected to give a little bit back to their "fans" in return for benefiting them so much financially. In no way to do mean that Watterson should be on Celebrity Jeopardy (he'd probably never beat Sean Connery anyway), but it might be nice if he did small things like book signings at local bookstores. I have that nice set of hardcover Calvin and Hobbes books, and I would absolutely love to have an opportunity to get it signed by Watterson. Sadly, autographs is one of the things that Watterson appears to refuse to do.
As someone who would probably be called a "recluse" by more than a couple of people, I can truly understand to desire to be removed from the limelight, but still, it's sad for those who adore his work that they don't have the opportunity to try and express that just a tiny bit.