Because if he makes that exact same motion same posture and the other player doesn’t bend over, that’s pure chest/shoulder height if you were talking about chin contact. You know, “game of inches” cliche.
We have the benefit of slow motion and hindsight watching replays of head contacts after the fact. Players aren’t psychic. With hits or passes or defensive positioning or everything else, there’s a degree of anticipation.
“Blindside” generally isn’t a thing. Hitting in the numbers is. He was starting in front/from the side. Most people would consider it unreasonable to only allow players to make hits skating through head-on paths. It’s unrealistic.
There’s an inherent risk of head contact for a variety of reasons, and a height gap can make a difference, among other things and often in combination.
The point of punishment is to deter the action that lead to a result, not magically the result itself.
If a player makes good hitting posture from a legit angle that, as far as any person can realistically tell in real time at their angle of vision at that speed trying to be physical, had a very real chance of making shoulder/chest contact... what behavior/intent are you discouraging?
Just ban hitting at that point. You can’t just look at the result alone. Head contact will always happen through a season with hitting.