Some more obvious reasons!
It was the end of the game
You were buying another VP card and felt the 2nd one had really earned the Hovel trashing
Something non-obvious
You might want your deck size to increase for Vault or Secret Chamber money in the case where you are drawing your whole deck.
Possession turn and you wanted the Hovel to be in their shuffle, though this doesn't actually work with the wording "I just bought a Province."
You could imagine deck states where your opponent has Possessions and you don't want to improve your deck, this seems pretty speculative and marginal in any case but I can see someone talking themselves into it.