like a broken telephone, everyone's got their own interpretation of "why tripods should not be used while at the sky park".
my guess (which is from my experience in hospitality) is that they know that there's an amazing view out there.
they don't want people to miss that view, but they sure don't wanna deal with their own hotel/restaurant guests complaining that the whole sky park's view is blocked because of a bunch of "photographers" are taking pictures.
you allow one to set up a tripod, there'll be a whole mess of them who'll do the same and it'll block the view, and create an eyesore for the others.
just my 2 cents