The fall of the NY Republican party began with the dismantling of the Nassau Machine in the late 80s/90s. Without the tons of banked votes guaranteed by the suburbs, the GOP were no longer able to crack the code to win a serious statewide race. Pataki was the last, and he was essentially on cruise control. When parties give up seriously contesting the big offices, they decline into their strongholds, and in doing so, tend to put off former potential voters. Focusing solely on small strongholds leads to more extreme voices getting microphones, which turns away more voters. The NYGOP today is more or less an upstate party + a few bits, which is what happens when the party pulled back from countless suburban towns.
It all just took a while to finally manifest in totality. That's how these things usually work out. Here's a good piece from 2010 on the topic:
https://twitter.com/SteveKornacki/status/1193877632275927040
