Many people on here and many indie game devs do this around a full time job, a family and even other hobbies too. There are only 24 hours a day and sometimes you have to sleep as well.
Personally, I do this because I love it! I hope my game will be a success, but lets be realistic, the chances of that are slim. But it does not matter.
I have also written a book with near zero chance that would make any money. I also recorded a few tracks in a studio with my band, again near zero chance of making any money. But we did those things not to get rich, but because we loved them.
I currently do a job I am not particularly fussed about, but I get paid well enough to pay the bills, provide for my family and save a bit. That is enough to allow me to do the things I love. And making games is one of them.
You are right, there is no massive pot of gold at the end of the game making rainbow for most of us. You know that your violin business is hard, it is difficult and challenging and takes experience, expertise and drive to keep it earning income. Why would you think the ‘business’ of entertainment and game-making would be any easier? The business itself is totally different than the making of games.
My advice would be that if you are in it just for the money, then your efforts might be better spent doing something with more chance of success (like your violin business) than game making. Earning a living at game making is as difficult as Acting, Singing, being a Magician or Comic, or any other form of entertainment.
However you are wrong that humans only do things for money. There is also love, whimsy, passion, desire, empathy, generosity and fun. I don’t play sports in my local team for money on Mondays and Thursdays, lol, the very thought. I don’t mow my elderly neighbours garden for money either. Nor do I charge my mum for visiting her. Yet I do all these things willingly and as much for my own pleasure as anyone elses.
Anyway, I wish you all the success in the world with your game, your violin business and your life in general. Just bear in mind, money might be a means to an end, but it is not the end itself.
PS I just realised the irony that you are posting this comment on this free Godot platform, an open source FREE game engine enabled by the voluntary and charitable contributions to the engine and to the NON-PROFIT organisation ‘Godot Stitched’.