Why am I doing this? Quick answer: I don't know. I do enjoy some of the camaraderie of riding with people, but that doesn't happen very often. Probably more than 90% of my rides are solo; there aren't a lot of people out there who don't freak out at the question 'hey, wanna do a real quick century?'
I like the mechanical aspect of working on my bike, though I get occasionally frustrated with my lack of expertise in certain operations requiring a certain amount of 'muscle memory' or finesse. I'm continually fiddling around with my derailleur adjustments and they're still not where I want them; I think I could take it in to a shop and they'd have it set right in five minutes.
The tactics aspect of riding appeals to me but there really isn't any way to learn them as a cat 5. If I ever upgrade to cat 4 then I could ride the 3/4 races and really start learning. But as an ultra rider, tactics other than 'keep pedaling' aren't really necessary.
Biking certainly get me out of the house, and I'm in the best physical shape I've ever been in. I do have some regrets that I got into this so late in life and often wonder where I would be now if I had been this dedicated one or two decades ago? I'm not going to kid myself that I could have been a pro, although I certainly fantasize about that (who doesn't?) but I would certainly be a much better rider now.
Of course if I was riding the last two decades, who knows what toll that would have placed on my body? Would I replace the lung-searing effort of trying to keep up with the Cat 5 group with chronic neck pain?
What do I enjoy about riding? This may sound a bit arrogant but I slightly enjoy the feeling of superiority over weekend riders. Call me shallow and insecure if you'd like, you're probably right, but there it is.
I also like to think that I'm still on an upward curve as far as month-to-month improvements go. Maybe I'll get discouraged when I finally plateau, which should be in a year or two?