It's also how it stops being a game.
When I'm playing D&D, I don't need roleplaying to transcend anything. I've been in professional productions. I know how to get into character. I understand how to inhabit the mindspace of another individual. I have been playing make-believe since I've been a toddler. If I wanted to transcend the character sheet, I would abandon the character sheet. I don't need D&D to play make-believe.
I do need D&D to be a game, which means that I can use rules in play to attempt victory. If the game doesn't support me using rules to find the secret door or convince the grand duke of the urgency of my quest, it's not meeting my needs.
It's still a roleplaying game, which means that part of the game is getting into that mindspace. But without the game, it's just roleplaying, which I don't need 900 pages of rules to do. It's fun and all, but it's not the reason I play D&D.
You see it as an imperfection leading someone to fall back on a lesser element. But to me, that element -- the dice roll -- is the point, and roleplaying is largely set dressing around the point. Without that roll informing the DM, this is just Bad Theater Hour in my living room.
A system that relies heavily on DM Fiat doesn't let me feel like I'm accomplishing anything. It feels more like I am trying to convince the DM to let me do something. That's not a game I'm interested in playing.