Players playing their moves out as they think best is their prerogative. If somebody does this repeatedly, I'll tell them that they don't need to generate $20 and 5 buys on their last turn when $8 is enough to buy the last Province for the win.
Everybody feels bad/bored from time to time when their cards don't connect and they have 10s turns, while their opponent plays 20 Action cards (in a timely fashion, but 20 cards take time).
If you think people are bloating their winning turn to unneeded length, you can resign. If you think people are buying more Grand Markets than they need, there is an easy way to get back at them: just beat them. You'll likey find out that a deck that buys a Province every turn is suddenly going to miss a turn, then a second where it can't do that, because the Provinces are now in your hand, instead of the Golds or Smithies that used to be there.
I see that you are annoyed by this behaviour, but I don't see it as a big problem. Calling the community shitty for that behavior is nor warrented, IMO.