It’s just cheaper. It has nothing to do with it being more listenable. Same with auto tune. It’s cheaper to have some mediocre singer do the track and fix it later. You don’t have to pay the great singer. And if you do get a great singer, you don’t keep them in the studio for as long. It’s just a cost savings. It doesn’t improve the music.

It's cheaper to do what? The thing they're getting for less money is precisely the improved quality or listenability. Their definitions of quality and good enough might be fucked up, but the intent and purpose is clearly to improve it up to some minimal level of quality, otherwise how are they judging a mediocre vs. great singer? How do they know when the great singer is done singing (sang a good enough take), or when they've tweaked the mediocre vocal track enough? The technological interventions change the ratio of cost vs. quality, they don't make quality irrelevant. If they did, you could just record the crappy singer as-is and save even more money.