I'm not sure what you mean. Isn't the whole problem that winning elections is heavily dependent on money?
So even you concede that it's not totally dependent. Boiling elections down to one problem is a gross oversimplification. Yeah you need money, but you also need a platform people want to vote for. You need good faith with your electorate.
What good is cash if you've alienated your base? What good is cash if you've already got 32x more than your opponent (Cuomo's $16MM to Nixon's $500k)[0]?
Right now, Cuomo's at a greater risk losing progressive votes than running out of money. The memories of Alexandria Ocasio-Cortez v Joe Crowley are still fresh in everyone's mind. Money didn't help Crowley there...
0 - https://nypost.com/2018/09/05/cuomo-spent-8-million-in-three...
Many fewer people vote in the primary, but perhaps those people are harder to reach, or perhaps who shows up depends heavily on money (or perhaps something else).
Also, I observe that politicians want money for more than their elections. They provide funds from their treasure chest to other politicians and groups. I wonder how much that use of money affects their fundraising and money's influence on them. (I think it seems like a source of corruption, and that money donated for the election should be spent on it or returned.)
So running too left can win you the primary but lose the general.
Cuomo is trying to move left but not too left to leave him vulnerable to a state challenge