Well the majority of artists make their money from concerts, not their records. Because they had rip off contracts. That has always been the case, even before the internet and people getting music for free. Even the few who became millionaires did not make as much from their record sales as the record label. It's even worse today with 360 deals where the label gets part of the touring & merchandising income. Many artists are in the hole to their label, because things like music videos are charged to the artist. That's what happened to TLC in the 1990s. They sold multi-platinum and the members didn't make much of anything and were bankrupt. Billy Joel's old manager stole a lot of money from him.
Also there's thousands of albums released every year and a very small percentage get any sort of radio airplay or popularity. Most genres are not played on commercial radio (gospel, folk, zydeco, blues, jazz, "world music", Hawaiian, comedy music, local bands, bossa nova, etc) and so their records don't get the blockbuster sales of whatever is mainstream popular. They have to constantly tour to make a living, same for many oldies acts. Since a lot of today's popular music is programming or is based on samples, there isn't as much demand for session musicians like decades ago. Some of the popular acts today make money from doing other things like acting or selling stuff like Rihanna's makeup line & Dr Dre's Beats headphones