...surely taking on challenging roles is more important than getting paid lots of money for doing very little.
Some actors look at their careers as just that...a career. It has very little to do with artistic expression but is more something that they stumbled into that is very financially lucrative.
I mean, I have a hard time believing that most career soap opera actors are in it for the artistic expression. Sure, maybe a lot of them just aren't good and that's the best they can get, but I know a lot of them stumbled into it and just love the money. How else could you be happy playing the same character for 30 years?