For those not aware, the 100Wh limitation is not Apple, but imposed on them by the airline industry (IATA)[1]
Anything over >100Wh && <160Wh requires airline approval at individual passenger level. Anything >160Wh is classified as dangerous goods and must be prepared and packaged correctly and put in the hold.
[1] https://www.iata.org/contentassets/6fea26dd84d24b26a7a1fd578...
The airline rules are a bit arbitrary. They have allowances for mobility devices but don't seem to take any extra precautions for them when they have bigger batteries. There are still a lot of dangerous gaps in airline safety when it comes to lithium batteries.
They're absolutely arbitrary. From what I've seen, one of the major problems is wild variation in quality. An 80Wh battery from six-random-letters-off-Amazon is going to be more dangerous than a 160Wh battery from a reputable manufacturer.