Zeff writes that WFP leaders are now rationalizing Cuomo's sticking them in the back and reneging on the promises he made to gain their ballot nod last year and avoid a third party challenge in the general election.
They're giving all sorts of reasons for why they endorsed him, but the real reason that they made the deal was this:
The party was concerned that if it did not back the governor, he would try to gut their organization. One method would be to empower a new party and convince several key union affiliates of W.F.P.—who had good relationships with the governor and depended on him for key contracts and wages—to join this new party instead. This would deplete W.F.P. of money and ground troops. And also leave its composition disconcertingly white and homogenous.
They also feared what the toll it would take on the party during the campaign (and likely after the campaign too, given Cuomo’s reputation for vindictiveness) to have to deal with a governor's office in permanent war-room mode.
In the end, they saw the deal as a necessity, and hoped Cuomo’s promises would at least allow them to argue after the fact that they had not given away their endorsement for free.
You do a deal with the devil, you get burnt.
WFP and Bill de Blasio both got burnt.
Cuomo reneged on his promises quicker than you can say Moreland.