How come New York city dosent have alot of theme parks?

There's not really space (or affordable space) in NYC for a theme park.  There is also not demand for a theme park in that area.  There are theme parks within an easy drive, and there are plenty of other great things to see and do in NYC.

It doesn't need them. There are lots of other things to see and do.

There was one called Freedomland, which was bigger than Disneyland, in an empty corner of the Bronx. After Freedomland closed, due in large part to the greater popularity of the 1964-65 NY World's Fair, the land became the site of a huge apartment house complex. Palisades Amusement Park, just across the Hudson River from uptown Manhattan, also became the site of large apartment buildings, a more profitable use of the land. Ironically, the park was a victim of its own success. It was opened by the local trolley company in the late 19th Century to create ridership for its streetcars on weekends. Parking space for automobiles was not an issue. By the mid 20th century, there were more cars than parking spaces, and park patrons parked on local streets to the great annoyance of the residents who complained to the town government. The town became less than supportive to the park, and the owners took the money of the real estate developers and ran.

Because other than existing parks, there really isn't anywhere with enough empty space to build one.

The land is too expensive.  Theme parks require very large grounds, plus equally large parking lots.  Plus, given New York's climate, they could only be open about six months a year before having to close down due to the cold, leaving the theme park empty and not earning anything.  There's a reason that Disneyland is in California, and DisneyWorld is in Florida--they can stay open year-round.

With that said, many decades ago there was Freedomland in the Bronx which was a theme park, but it eventually closed down and a huge apartment building complex took its place.  Also, in Coney Island (which still exists, but not as a single theme park), there was Luna Park, Steeplechase Park, and Dreamland; now all gone.

For those who want to go to a theme park, there's a Six Flags in New Jersey, about an hours drive from Manhattan.