No connections? Virtually all activities everywhere are carefully planned by the Korean labels. These groups can't even crap unless they have their handlers' permission.
What actually happens on the ground is besides the point. Once again, I'm referring to contractual obligations. There is nothing stopping a successful K-pop group from signing with Interscope, as you yourself pointed out. The issue is that American labels are not interested in them, because there's little chance of them succeeding.
And why would JYP Entertainment or SM Entertainment refuse to allow a successful group like SNSD to sign with an American label, if that's what it takes to achieve success? Like you said yourself, success in America isn't possible unless you sign with a major label. So it seems like that's exactly what they'd do (and exactly what happened with SNSD). Yet SNSD hasn't succeeded in America. Care to explain that?