Basically the tier is overcentralized, with the same group of Pokemon used all the time. Playing the tier is sometimes like listening to a broken record for some.
Also, many Pokemon struggle to even be in the ubers environment, with powerful Pokemon lurking around everywhere. It's hard to find a Pokemon who can fit into the tier without being outclassed by something else, which explains to overcentralization in the tier.
I noticed that Ubers seems slightly more weak to hax after laddering for a while. Your counter or check could be KO'd thanks to hax and usually most players only carry one counter or check for a specific Pokemon.
Also, many Pokemon struggle to even be in the ubers environment, with powerful Pokemon lurking around everywhere. It's hard to find a Pokemon who can fit into the tier without being outclassed by something else, which explains to overcentralization in the tier.
I noticed that Ubers seems slightly more weak to hax after laddering for a while. Your counter or check could be KO'd thanks to hax and usually most players only carry one counter or check for a specific Pokemon.