Because not making the move means you have zero chance of making the playoffs with your under performing goalies currently on your roster. It is not about paying just barely more then the next guy, it is about getting a goalie that can give your team the quality it needs in net to make the playoffs. If you don't see it that way I understand, but I would love to know who your goalie is on opening night?
It's an empty ultimatum you're threatening. Considering where Colorado & Vegas were this point last offseason, when people were making "who'll finish with a worse record - Vegas or Colorado?" threads - how did that turn out? This team will be reinvigorated playing under a new boss, so if all you have is predictions of doom for the Islanders moving forward, I suggest finding something else to say.
The assets we have - two 2nds, Nelson, Ho-Sang, Dal Colle, potentially Pelech, those will be the likely assets bandied about to find a goalie. With Sorokin playing out his KHL contract, I'll take the chance underpaying for a Lehner, or a Jimmy Howard instead of a high 1st rounder for Grabauer.
Want one of our picks? Offer up a youngish top-4 defenseman. All we offer is the best of luck trying to find another team willing to pay a high 1st for Grabauer.