Well, yeah - generally, musicians do not get "rich", or at least not overnight. Entertainers, on the other hand, that loosely use music as their vehicle, can get absolutely mind-blowing stinking rich. Very rarely do you see true musicians that actually put out real music ( and I know that the definition of "real music" can be widely interpreted ) get filthy stinkin' rich. Paul McCartney, Stevie Wonder, Springsteen, Sting, Paul Simon, people like that come to mind. But notice how almost all rich "musicians" had to make it back in the 60's and 70's when popular music could still be actually "musical"?
I mean, Britney Spears or Rhianna most likely have bigger checkbooks than God these days, but suggesting that their first priority is to be the absolute best, most skilled and accomplished musician they can be is a stretch. I'm sure they spend some time on it, but I'd bet dollars to donuts that they worry way more about their looks, dance choreography, video production values, etc. The music is incidental to the "product".
But real musicians? See any super rich jazz cats in your neighborhood?