You could say the same thing about Weave and any other UUmons in the A ranking though. Lokix is a Pokemon that requires a very high level of skill to pilot and requires a good amount of support from hazard removal to keep CB variants alive, special wallbreakers to handle physical walls, and Pokemon that can attempt to handle quad resists to FI that aren't actually super uncommon. Ladder isn't using it because the ladder is not full of Pinkacrosses that can always make Lokix work.
You absolutely can say the same thing about a lot of good UU mons, you're right. That's why people
do say the same thing about a lot of good UU mons.
There are a lot of mons that are legitimately excellent in OU that don't or didn't get OU levels of usage on the ladder despite their excellence, because ladder tends to lean more towards certain types of mons than others.
Pecharunt, Moltres, Iron Treads, Zapdos, and Iron Crown clawed their way into becoming OU staples over the course of many months. Mons like Lokix, Sinistcha, Tinkaton, Weavile, Galarian Weezing, Scizor, base Ogerpon, previously Ogerpon-Cornerstone, and Hydrapple are
greatly respected by many great OU players
, see or have seen plenty of tournament usage and success, and even pop up occasionally on the ladder and get juuuust shy of the usage needed to be OU proper. Meanwhile Meowscarada has been clinging onto OU usage ever since DLC2 released, even though all the mons I mentioned earlier are significantly better and/or easier to fit on teams.
At the end of the day, OU's been experiencing an odd sort of "low-tier Renaissance" in the last half a year or so, because there's a large number of
good fucking mons in this metagame that cannot get the usage they deserve because you can really only use so many mons 4.51% or more of the time.