Depends how far back you want to go.
I worked with guys a generation older than me. One clarinet/sax player worked in the "house band" at the Elmwood Hotel in Windsor Ont. Canada, in the 1950s. He had a wife and kids and a mortgage. He worked 6 nights a week and name acts like Ella Fitzgerald and Benny Goodman came through the town on their tours across N. America.
That's when professional musicians were musically "literate", so many acts showed up with just their soloists and boxes with their "charts". One rehearsal and the show was ready to go.
Sometimes not even a rehearsal. Chuck Berry was famous for just showing up minutes before he was supposed to go on and using whatever musicians happened to be around. Apparently, lots of not-yet-famous musicians were in Chuck's backup band at one time or another, Springsteen among them.
My best friend (son of a session musician) tells the joke "what's the difference between a session musician and a pepperoni pizza...the pizza can feed a family of 4".
Yes, but not a good living.