I’m sure there are good wineries in Long Island, and I’ve read the quality has improved.
But early on Long Island wineries had a very Cabernet-focused approach with heavy oak, which was just a bad match to the terroir. I think these types of wines are still made in some quantity. The fruit is just too thin and not ripe enough to support such treatment.
Also, they had a bit of a captive audience. A short train ride from NYC, most producers could sell everything without really worrying about quality too much. And prices were (and are) high as a result. It’s popular with the wine tourism and wedding industries.
I think there have been efforts in recent years to plant grapes more appropriate to the high-humidity, lower ripeness climate. At least that’s what I have read. At some point, I will try again, but the lack of soil variety, the weather/humidity and approach of winemakers gave me and many a negative impression of the wines from Long Island.f