Dave, US Sailing is directly represented on the ISAF Council that made the decision. Whether they lobbied other nations I don't know, but the US Sailing delegates did have an explicit voting strategy to favor the keelboat over a multihull in the event that one of those had to be dropped.

I'm not sure about ISAF funding, but US Sailing get their Olympic program funding from three places, none of which is member dues - donations, sponsorships and the USOC. The latter is dependent on actual medal results.