That really, really isn't true. Yes huge celebs like Tom Cruise are very wealthy, but plenty of celebs are not rich. Actors are rarely wealthy unless they are major Hollywood stars acting in studio movies or on Marvel contracts. Or actors on American TV shows who are on longterm contracts.
I know and have worked with tons of actors who regularly play leads in theatre productions and are regularly on TV, but still work shifts in day jobs on the side because they wouldn't be able to afford to live in London on what theatre and TV pays.
Even household name TV actors or TV presenters not on golden handshake deals earn enough to live nice comfortable lives, but that's very different from being super wealthy. Most British household name actors I know live in normal houses or flats in London, take the tube, shop in Tesco. They can afford to buy a nice-ish house and maybe send their kids to private school, but they certainly couldn't afford the whole Tom Cruise enchilada with bodyguards and gated mansions. I mean, I know household names who never stop complaining about their mortgages. We're not talking rich here.
Music celebs like pop stars don't make money unless they write their own material (meaning they own the rights) or do a LOT of touring - the money in the music industry mainly comes from touring, or from licensing song rights for things like TV commercials. The music industry is extremely exploitative to the point it should be illegal; young popstars often end up broke and bankrupt because they don't realise they have to pay back everything that's spent on them, even music video costs. You can easily have a #1 single and earn nothing if you're not credited as a writer.
As for ego, it really depends so much. Reality show stars skew more egomaniacal. Most actors actually don't have big egos. There are plenty of actors who are very shy and introverted and tolerate fame because they love the craft of acting, very shy people often love acting because it's a chance to lose themselves inside a character.
What part of the entertainment industry to you work in?