It feels like Poly hotel room availability has been pretty thin ever since they revealed the room makeovers and opened reservations, no matter the time of year. An already popular resort now made even more popular with what is a generally well-received renovation (in contrast to what may not be as popular a renovation at CR?).
So I suspect it’s a combination of popularity, large numbers of people who aren’t traveling/can’t travel now but are rolling vacations or making placeholder reservations, etc. Poly CL (not an insignificant number of rooms) also doesn’t have a reopening date yet and we don’t really know how that room inventory is being handled. Presumably they could open Poly CL sometime next year and some with current standard Poly rooms would move their reservations to CL.
Just me speculating though.