If becoming one of the world's wealthiest musicians requires prioritisation of your brand over improving the world in ways

There is no if, that's generally how it works. As I said, there are always exceptions, but when you are a super famous pop star on a major label, you probably ended up there because you do what your label/manager tells you to do, not because you alienate part of your fanbase/boss/business associates.

becoming a wealthy musician is absolutely a sign of moral failure.

I don't even fundamentally disagree, I just think you are setting a moral standard that unfortunately will not be upheld by a majority of people if they were given the chance, which means you are setting yourself up for disappointment. Most people would choose not to swim against the current and take a "neutral stance" (or whatever stance their boss wants to them to take) over risking their career, that’s just how most humans work.

That’s why it is useless to expect CEO’s, politicians, business owners, etc, to act according to your morals. They act based on incentives, and the only way to make them act according to your morals to some degree is by forcing them to.

It's also not even necessarily detrimental to the brand to associate it with acting morally

If your entire brand is “I’m a pop musician who makes unprovocative pop music for everyone and don’t make public statements about controversial political issues“, it can absolutely be detrimental..

I really don’t think it’s that surprising: Venue owners band together and tell that multiple concerts of your huge tour with 15 support acts is essentially chanceled unless you kick one support act. For pretty much any tour promoter/organizer/manager, the decision is obvious..

that only made Dolly Parton more beloved.

To be honest, I’m hardly familiar with Dolly Parton, but wasn’t she famously silent on controversial political issues? At least I found this quote from her sister

"You know, I’ll tell everything, and I like everybody know what I think about it, not her. Because she’s a good businesswoman. She’s a good businesswoman.”

I also didn’t find any comment on Israel or Palestine from her, so I’m not sure why you are using her as an example, maybe I’m missing something? Because it seems to me that maybe she was beloved across the political spectrum because she didn’t publicly speak out on controversial issues..