Because composers are artists and (I imagine) making art is not like a regular job. I know I would put a lot more effort into my job if I had to create something that people will enjoy experiencing and remember for a long time instead of spending all day sending e-mails and filling spreadsheets.
Honestly, I disagree with this. Some soundtracks should "go hard", like Doom, Jet Set Radio, Bomb Rush Cyberfunk, ULTRAKILL, etc.
SimCity does not need a soundtrack that goes hard, nor does The Sims. If anything, a soundtrack that "goes hard" would distract from the gameplay. SimCity doesn't need a soundtrack that makes you wanna dance or rage. It needs a soundtrack that makes you relaxed. You're here to run a city, not destroy it, even if most people do that anyway.