I was thinking about that in response to the other reply below. I think it's definitely based on value; at some point you realize that you'd be happier doing something else. At work, you don't have the same calculation because it has to be done and personal rewards are not the only motivation.

I've also found that how intellectually rewarding my day job is (and how much agency I have) has a direct affect on my hobby development. I have a lot of creative freedom and interesting projects at work right now so I care less about coding in my spare time. I only have so much free intellectual energy to devote to something.