This feels like a question that would really benefit from talking to some musicians, instead of basing your framing on biopics and data. Some musicians are in it to be rich and famous, and become computer programmers when riches and fame leave the picture, but most of them are musicians because they like writing and playing music more than anything else. I'd bet that Of Monsters and Men is perfectly happy to make an okay living off of their remaining fanbase, because they still get to tour and make new albums. They might be even happier about it if they could get a second hit, but there are so many musicians who have never had a breakthrough hit, who make a happy living opening for other bands, meager royalties, Patreons, etc. Basically, this post assumes a causal link between chart success and life satisfaction that probably doesn't exist.