All of the folks you mention had legitimate credentials as mainline classical composers. However, they also needed to make a buck from time to time - so wrote popular dance music, songs, and film scores. Some of those film scores were in fact serious classical works that they reconfigured to fit the needs of the film. Heck - we all grew up seeing Harpo Marx play a lovely solo - right in the middle of a film that it had nothing to do with. I have been a classical musician professionally since 1973. We have played thousands of GIGS, besides serious concerts. Many of those gigs were weddings - where the ceremony required classical music ( often cut to fit time allowed) - and then the cocktail hour, American Songbook, musicals, etc. Nino Rota played both sides of the industry - as did many others. I taught middle school and Hs music for decades - so I could afford to retire in my fifties with my husband ( who did the same thing) so we could decide even MORE time to our concert work. Risky Korsakov collected tools and taxes. Heck, Sir Isaac Newton worked detecting forged money for the Crown! There is a local dance band here called Bill's Toupee - not because Bill is bald - but we all make money as we need to - like the character in SIPWG said - "Work is what you do for others - ART is what you do for yourself."