It seems to make perfect sense, given that the tier names are "OverUSED" and "UnderUSED." Back in RSE, the tiers were subjective, so people just put relatively bad Pokemon in UU, and everyone made the association "UU Pokemon = crappy Pokemon." In DPPt, the tiers actually started being based on usage, and hey, some relatively strong Pokemon were in there (everyone gawked at the idea of Milotic being UU, but that eventually started making sense to people).
A power creep in OU results in a power creep in UU, and some Pokemon that were clearly OU in the last gen fall into UU in this gen (again, think of Milotic from Gen 3 to Gen 4). I think it seems like a pretty natural progression for Snorlax to fall into UU, as it wasn't even that used in OU at the end of last gen. Once things stabilize, we'll see what UU looks like; certain Pokemon will get banished to BL, certain Pokemon will remain UU, and the tier will look very different than it did last gen. People seem to be all up in arms about the tier system, saying it doesn't make any sense, before things have even remotely stabilized. And what seems so out of place? Nothing, except for the theoretical possibility of Salamence falling into UU (even though it could easily become borderline if that happened). But 1) I just don't think it'll happen (Salamence does a mixed set better than any other dragon this side of Rayquaza), and 2) there are more good Pokemon out there...did you expect UU would be the same this gen as last, only with a few new Pokemon and finally having Electivire and Weavile in it?