If placements mean nothing whatsoever, why do them at all?

I am ok with being demoted after placements. I don't think the system in place is correct, but as long as it is the same across the board, that is fine.

But if placements have zero effect on your MMR afterwards, why go through the process at all? From what I've read on here, and what I've seen in my own standing, they aren't even part of the equation. So just throw me in bronze 5 and let me start working my way up rather than making me play 10 games before I can even get to the bottom of the ladder.