Because it being centralizing is something OU needs. In this Gen, we have something close to that pipe dream of several Pokemon being viable. That, in turn, makes it impossible to create a team that covers everything and makes some matches won not by who played more skillfully, but by blindsing the opponent with more esoteric stuff.
This inconsistency is what made Smogon transition more towards tournaments rather than ladders.
Landorus-T centralizes the meta, and thus limits the amount of threats that need to be accounted for while team building.
Several atempts of decentralize OU have been made before. Usually, the meta re centralizes around a new threat, or so many new threats appear that it becomes impossible to deal with them all.
Of course, that's my perspective as an outsider that more lurks than plays competitively. If in your experience Lando T is busted it might as well be.
As a smogoner, this sounds about right. I haven't played OU since gen 4 (I used to focus on Ubers, now Battle Spot), and afaik, most of my pals tell me that Landorus-T is more of a balancing force than some disgustingly broken threat or anything.
Also, I'm curious about what people mean by "they want more versatility". Like, there's already... 50ish Pokemon or so including megas, that are OU, and there's even more than just OU Pokemon viable in that metagame, take look at this!
https://www.smogon.com/dex/sm/formats/ou/
I think people need to realize to that there's more than just Smogon's OU. Gamefreak has 2-3 different offical formats of their own each year that differ drastically from the usual Smogon stuff. And for people that want to see a different set of mons, there's usage based tiers below OU, like Underused, that were basically made specfically so people could see different sets of Pokemon.
And that's not getting into the more niche, strange formats out there, such as Gamefreak's seasonal Battle Spot Specials, or balanced hackmons!
I don't mean to sound insulting with this, but I can't help but feel like people who complain about not enough Pokemon being viable aren't really that intune with competitive Pokemon. It isn't perfect, but I don't think a lack of viable Pokemon is really one of problems.
