>>47782857Because OU is supposed to be the primary tier that all the tiers below are anchored to. For example, Quagsire at one point had 60% usage rate in Ubers because it was the sole counter to Zacian-C, but Quagsire wasn't sent to Ubers. However, if Quagsire had 60% usage in OU, it would immediately jump to OU on the tier shift.
This means that a Pokemon could have 200% usage in OU (guaranteed to be on both teams) and still not get sent to Ubers unless it was suspected and banned. Landorus hasn't even come close to the monsters of some earlier gens that hit 50, 60, 70, sometimes even 80%+ usage. Snorlax had, iirc, 120% usage in Gen 2 OU for a long while. Tauros had similar usage in Gen 1 OU. Tyranitar was equally as prominent in Gen 3 OU.