Because, often (though not always) you have to write in a different way to get them. It is hard to write well enough to make money purely for pleasure, as the editing/etc process can be a grind trying to make everything smooth and pleasant to read. And with caveats the writers that are most famous tend to be ones who write big L Literature, which rarely makes significant money but is the stuff you hear about on TV in the news etc.

There are exceptions but it tends to require more than a little bit of luck to hit the zeitgeist in a way to work out. Take for example Brandon Sanderson. Outside SFF I doubt almost anyone has heard of him but dude makes millions.

Because without a priority, you have no means to make a decision when the goals conflict. If what's most important to you is having cake, you might have to limit how much of it you eat. If you instead value eating cake more, you might have to give up on the idea of keeping it.

Actually Fleming became famous too, but most of it was posthumously. Maybe one should ask oneself what one wants to achieve first.