You started from the wrong conclusion that if you can sing you should be able to live from it.
In any market I can think of at the moment, you have to be good. And if you're good, loads of people want what you sell.
You also made the mistake of assuming a (good) musician lives off selling songs. They don't.They also have videos, concerts, tours, endorsements, all kinds of stuff.
I'm not saying they shouldn't live off it, but arguing that if you can sing and bought the equipment you should be able to live off it is (IMO) incorrect.