I have always capitalized on my hobbies and while I have never fully paid for them with sales, I always supplement them in some way. Problem is always coming back to labor, and the fact that I can make more money doing other things. It's all relative though. When I was less financially secure, I made a lot of side money from my hobbies which paid bills or bought new tools or even paid for the next project. Today I wouldn't spend 100 hours in the shop to earn a thousand dollars on the side. It simply isn't worth the trouble any more.
It is amazing how many people out there will pay several thousand dollars for something and after a few months never use it again. Hot Tubs, Pool Tables, Arcades, Jet Skis... Most consumers will buy these high dollar items, use them for a few months or a year, and then never touch it again. But any business that sells these sorts of things stays in business because they work the business end of it, not because the owner likes getting in the shop and building them. The guy who actually makes the luxury items usually gets paid the least.
I've always wondered at how heating oil is still a thing. It seems so archaic, something out of the 1800's. Natural gas is the heating choice up here in the NorthWest. No way you can heat anything on electricity for cheap, so NG is the only good option. But I guess if you have entire cities that were never piped for NG, then a tank of oil in the basement is the way to go...
Finally, it is one thing to be the kind of person who can look at a water heater and see simplicity and have the tools to re-pipe to make the new one fit. Most people are simply not capable of that, and hence need someone to do it for them. The older I get, the more inclined I am to hire that stuff out too, regardless of how simple it is in my mind. I can change my own oil too, but I haven't done it in 20 years. Hell, I even bought an extended warranty on a couch recently. All relative...