It seems like your vision is hampered by your (lack of) experience, maybe?
There's plenty of people like me, and my fiancee. I'm a full time mostly session musician who does some orchestration, who makes a very good living. My fiancee is a first call session flutist who's also very successful. I own my home, she owns her condo. Both of them are paid off. (We live in NYC so it wasn't cheap!). Our late model cars are paid off. Yet somehow neither of us have a desire to have kids but we're both successful (and became successful early on) and are very happy. I'm in my 40s, she's in her 30s.
The only other people we know are also full time, professional musicians because of the circle we work in and the majority of them are in their 40s and 50s and married and childless and very happy. They're all pretty successful. It's not uncommon.
I get that maybe you don't work in that circle so you don't see that side - the successful musician who makes a very good living, who's married and childless and happy, but it does exist. The fact that you keep trying to shoehorn your views into two sides - the happy, married, successful family man with a good day job or the lonely cat lady/man who's a struggling musician is far from the only two options out there.
In fact, when my fiancee and I got engaged, our engagement party guests consisted only of full time professional musicians since those are the only people we socialize with and we had at least 80 people at our party and they all make good livings and are successful at what they do. I keep hearing the stereotype of the musician who struggles and is poor but again, that's not the only way you can end up. There are a large amount of very successful, full time musicians.