As a native English speaker I have a real problem with “almost“ and “exactly” in the same sentence, but... 🤐
There is a logical explanation if we discount those unfortunate watches with completely smashed faces which look like they got hit by a truck. This requires understanding two basic engineering facts,
1. Any crack in any material will tend to propagate along the path of least resistance.
2. Any change in physical properties like thickness, curvature, angles, radius of corners, etc will create some kind of local change in stress and the strength of the material. In other words, almost any design will create a zone where a crack is likely to follow a similar path, and this is an unavoidable fact. Increasing strength in one weaker area simply moves the weakest point to somewhere else like a game of whack-a-mole.
I said “almost any design”. There is one geometric shape which avoids this weakness. The big problem is that a seamless hollow glass sphere with constant wall thickness is very difficult to fabricate, even more difficult to get the working electronics inside, and completely impractical to wear as a watch. Maybe that’s why Jony Ive didn’t go that route.