Skeet was originally shot from a low gun position, and maybe with a delay, so the outgoing targets were shot from a greater distance than today's American skeet, so some choke was needed.
I always preferred some choke in my skeet guns, but Winchester apparently didn't agree, as the later 101 skeet guns were cylinder bore in all gauges. I don't recall any champions shooting 101's in those days though. I like 0.004" in the 12, and about 0.005" in the 20 and 28, with 0.007" in the .410. I first shot into AA class with a Remington 3200 fitted with tubes by Claude Purbaugh, and they were choked pretty much as above with the exception of the 20 ga tubes which had 0.017" of choke.
