Having ridden on subway vehicles in NY, Washington DC, London, Munich, Frankfurt, Berlin, Hamburg, etc....I can say that when you have seats that go along the window....all guys do it. When you have normal seating...guys typically don’t do it.
Having ridden many of those same subways, I agree. Part of the issue is, as noted above, the low seating height. The other factor in play is that the inboard-facing seats are usually at the ends of the subway cars, near the doors - where most of the ingress/egress traffic bunches up. I think most men are just trying to keep their feet and knees out of traffic, and they subconsciously "spread" while doing so.
I tried it, and it was waaaaay too big.