(1) Tactically, while the liberals are still in power, the NDP has some sway. If they forced an election right now, they would end up being a largely-voiceless secondary opposition party. Of course, you can only really exercise that power if you're willing to topple the government otherwise it's all just noise. So from their perspective, it's a fine line to walk.
(2) Personally, I'm hoping that between now and when the writ eventually drops, PP will make such a fool out of himself that he becomes too sour to stomach. At a minimum, I hope that this forces him into minority territory. (In my opinion, the ideal situation that would result afterwards would be new leaders for both Liberal and NDP and a short lived conservative minority.)