A softer make accessible sound means a larger audience which equates to more exposure and money. We may not like it when our favorite bands do it but they’re not only doing it for artistic reasons but for livelihood reasons as well.

For example, I hate that my once favorite band PWD essentially “sold-out” but they’re more successful now with that new sound so I can’t blame them. I’ll always cherish the old stuff even if I don’t necessarily vibe with the new. Also, the heavier and more technical stuff can get difficult to play and keep up with as a band gets older so they may have something to do with it as well.

TLDR: Softer sound usually equals more money so that’s usually the reason