Going back to the treadmill, they played 1 Right Price. For them to stop tape and replace the treadmill with...let's say a bedroom set, that would not only require a look at the inventory but also a new price tag. If it were a game like Bullseye or Master Key where you can win a nice prize but don't need to know its price to win, I would understand doing a swap.
But I imagine having to go to the inventory sheet or warehouse to find a comparable prize, plus find or create a price tag is way more work than the show wants, considering they pretty much still do things live on tape.