Steerer tube snappage!
U understand exactly what you are saying. Problem is the maths does not explain it.
If it was just down to exceeding the 'strength' of the bar during a move then bars would not last past the first move if you get me.
It is down to work hardening in alloy bars.
Steel bars snap because they are either under-engineered or they have a fault in them.
Under engineered as in the flex is past the elastic limit, or a fault in the tube or weld.
As you know as long as you don't exceed the elastic limit in steel you can flex it effectively forever.