The History Man pretty much nailed it.
I'd add that I skip work some days and do a full day of riding as an act of rebellion against what is expected of a married, father in his early 40s.
After wasting too much time working (and not riding) in my 20s and 30s, I'm now determined to use the rest of my time properly, not doing boring shit like working or watching TV.
The main reason, of course, is because I enjoy riding out in the wilderness and it should be a good investment in future health and a longer life.