Why would a Cessna 182T not enter a stall?
I think this is more common than you might think in a C182. The 182 is much more nose-heavy than a 172 (which is particularly noticeable in the flare) and this seems to limit the amount of upward pitch authority the elevator has at low speeds. The only stalls I've done in a 182 are much as you described - you can hold full back-elevator and you just sort of sit there sinking.

Spinning could be an issue if it becomes uncoordinated, but a 182 is a very stable airplane and unlikely to enter a flat spin unless the CG is beyond the aft limit or severely uncoordinated. Perhaps someone else can weigh in further on that possibility, though.