As I have said over and over and over again, if you have any proof for that claim, you should produce it.
I notice that Wikipedia is now claiming that the party's "headquarters" were in Buffalo, New York, but Buffalo is definitely not New York City.
The Free Soilers were strong in Western New York. First, because it was a very reform-oriented region. Second, because most people in Western New York had come westward from New England or had relatives who had moved further west. Buffalo was a gateway to the Northwest and the fate of the territories was a major topic of conversation there, as it was further west. Third, because the New York Democratic Party was split and the Free Soilers felt that if they nominated Martin Van Buren they could carry the state.
The party's 1848 convention was held in Buffalo, and the 1852 convention was in Pittsburgh. I don't see any evidence that the party had its headquarters in New York City, though you keep on making that claim.
Let me conceded the point about whether it was New York city or some other city in New York, but the larger point I am making still remains. Why is it located in New York instead of Kansas? Why is it any business of New York what transpires in lands over a thousand miles away?
Also, if you've been looking at it, did you see the racist motivation behind it? These were no friends of slaves, they simply wanted black people kept out of the territories.
When you look, you find out over and over again that the primary objection to slavery was an objection to having blacks in their racist white society at all!
This is something they never taught me in history class, and I very much doubt they taught anyone else this either.