Not everyone is a creator editing/rendering 4k videos. For the typical surfer/office worker/gamer QLC drives are fine because they rarely need to dump 50+GB of writes at a time. What you're suggesting is basically "ban all atom processors because they're criminally slow!"
So consumer SSDs now depend on a limited dynamic part of flash being used as SLC to cache writes. Just that this dynamic part mostly gets smaller the fuller the device is.
And as soon as you do anything with large writes you will hit a brick wall of slowness, on full devices sooner then on empty ones.
And I bet the vast majority of people basically never do >10GB writes at >200MB/s.
But the information about the limited write cache never gets mentioned by the manufacturers. So people that actually need to write large amounts of data from time to time, fall into a performance trap.