If someone isn't resigning in a game where they've clearly lost, the the other person has every right to play it out the way they want to play it out. Clearing out pieces when you're low on time is a sound strategy, because if you get enough of them, the other person will only get a draw if you run out of time rather than winning it on time.
No-one is forced to resign either - if you want to keep playing hoping maybe that your opponent will blunder and give up a stalemate, that's fine too. But you can't also then complain about how your opponent plays if you're refusing to resign in a clearly lost position.
Most people who play on here are really sadistic. They don't try and pin during the endgame, they go after every piece clearing the board. I have had players run out of time because they were too busy clearing your pieces. It's really sad, and a lot of them don't have pinning skills. Some players also wait until the last second to checkmate you. Really disheartening for newer players.