The problem is that a huge noticeable percentage of DMs, players, and writers did use alignment monotonously and restrictively.
I have yet to see any evidence that is the case. No surveys, no widespread polling, no beta test feedback, nothing which showed there was a "huge noticeable percentage of DMs, players, and writers" who used alignment in a particular way which was either monotonous or varied, restrictive or expansive. I have seen zero reliable data on its use. Have you seen any real, organized, standardized data gathered by WOTC on this topic?
That's why there is backlash against alignment.
I don't think there is backlash based on actual usage data. I think there is backlash based on theoretical concepts, mostly surrounding papers speculating about connections between alignment, D&D races, and real world races. I've seen no data that speculation was substantiated by the consumer base usage of alignment. Again, I could be wrong, is there such data you've seen?
And until fans who use alignment correctly acknowledge its missed by others and promote corrective language by WOTC or teach themselves, it will keep being used incorrectly and eventually be removed from the game.
The "it's not my problem. I know what I'm doing. Sucks for everyone else" mentality frequently seen in the D&D community will get sacred cows slaughtered at the Altar of Undereducated Fans. Especially since 5e flooded the game with new fans.
You have to first prove there IS a problem, and then that your solution is the least invasive solution of the set of options to address that problem.
For example if the problem is humanoid races, then removing alignment from adventure NPC entries isn't necessary, nor is removing alignment from PC character sheets, nor is removing alignment from many monsters like a Beholder.
You can't argue on one hand "Orcs with set alignment is an issue because of real world implications" and on the other claim a Gibbering Mouther suffers the exact same alignment issue when it does not. The least invasive solution would just be to remove alignment from humanoid races and then decide if the line stops there or needs a few other corner case "monsters" to be addressed due to potential human comparison.
Unfortunately what I have seen a lot of is "Some humanoid races like orcs have an alignment problem," which is a problem which at least has some substantial theoretical evidence behind it; and then people draw from that rather small subset of problems an extremely broad and overly expansive solution of "so let's remove all alignment from the game entirely." And when asked why people would take that extremely expansive solution to a problem which makes up a much more minor sub set of uses, I see a lot of "because alignment sucks" arguments. Which isn't, in any way, germaine to the legit problem that was being pointed out about orcs.
You thinking a rule sucks, without something more, isn't a good argument unless a large number of consumers who play the game agree it sucks. Because let me tell yah, there isn't a rule in the book which a small but loud number of people don't think sucks and we'd have no game if that's all it took to change the game.