I like to. Always have. By the time I was 19 I was riding a classy 531 frame, all Campy, tubular tires. Europe. Long trips throughout the east US.
At this point, I can't come up with anything different as a reason. Does make me feel good, keep flexibility, spend time with my wife (who is keeping up these days - she'll be faster eventually I suspect). But these are just things I notice. I suspect I simply like it because that's the way I am. I like loafing along, riding fast on the straights, dropping fast and hard, turning hard, getting out of the saddle and climbing, clicking methodically through the gears, seeing the vista change, feeling rain hit my skin, feeling my muscles burning hotter & hotter and my breath ripping in and out, feeling the tires rolling. I just like it all.
Maybe because cycling induces mindfulness.
I suspect I'm almost as good a cyclist now as I was 30 years ago. Endurance, peak power, bike handling are a bit down, but not really very much.
I missed the 10 years my back kept me off the bike.