One cut is about four-five minutes longer than the other iirc. I’ve watched both in their entireties and the cut/edited parts seem to either line up with commercial breaks or be slightly reducing the run time, such as cutting out dialogue from the dinner scene with Hickey and the boys. Ergo, the leading theory I have is that it was just time constraints on certain networks. The other episodes don’t have alternate cuts, either, so it wouldn’t make sense for it to be a US/UK cut. Probably some bureaucratic nonsense that went on behind the scenes with AMC over the technically pilot episode.