I've quite literally never once seen a musician expend effort toward learning marketing and business without finding success.
I also don’t know all your marketing knowledge. Maybe you know a whole set of things I am completely unaware of.
What I do know is success as an artist seems to be a weird blend of savvy, talent, luck … and who knows what else.
I have a bad reaction when people make blanket statements like you are doing, because it has a hint of victim blaming.
You initially added nothing to the conversation, except for a very brief and vague claim about how you may know some people who contradict my own experiences. So, I'm not sure what kind of response you were hoping for, but a little snark never hurt anyone, and you're overreacting to it.
If you have an actual example of a musician who studied marketing and business but was unsuccessful, I'd love to hear about it, because I've simply never seen it happen.
I genuinely think you might have access to knowledge or perspective I lack, and I would be very curious whether there are specific materials or resources you would recommend.