First, finances are most of the time just a roundabout way of trying to be happy. So in a way doing things that make you happy directly instead of doing things hoping to gain money for that activity and then spending that money to hope to gain happiness will never work the same (provided you are not starving).
Second, many people on this platform, me included, got good at the things they do for a living, because they did it for fun (and sometimes still do). Going for the fun project helps you learn faster and better. It might be "the wrong" thing to learn, but who is even able to judge that?
I live in a nation where we consider it normal to not let those living around us die of starvation or illness. That includes me.
Also: I made that caveat and you skipped right past it. Everything is a gradient of course. I am not suggesting you have to never follow some discipline and always go for the fun route.
Second, many people on this platform, me included, got good at the things they do for a living, because they did it for fun (and sometimes still do). Going for the fun project helps you learn faster and better. It might be "the wrong" thing to learn, but who is even able to judge that?