That’s not really true at all. Artists generally really do care a lot.
The big promoters try and get away with as little expenditure as they can to maximise profits.
It’s perfectly possible to get an arena to sound great, but it means the promoter hiring the appropriate PA system. Which is a big cost - so things are almost always trimmed down, at the detriment to the sound. Even acoustically close to perfect rooms like the Bridgewater Hall can sound shit if the right system isn’t used.
Big venues are often dry hires - just a big empty box, and the promoter has to sort the PA, lighting, etc.
(I do this for a living)