Based upon what I have read about Tim Cook and several Apple engineers, they are paranoid about security. That is, they don’t want anyone messing with their devices and getting away with it. They especially do not trust the US intelligence agencies, and have suspected them of trying to sneak stuff into phones that were held for inspection at airports.
I also suspect that as Tim is a sort of zen master of logistics, they figured it was more efficient to put the chip on the battery, repair be damned since the savings in manufacturing outweigh the few instances they reckoned a phone would have its battery replaced. Done right, most will upgrade long before the battery becomes an issue.
Considering the number of devices Apple makes and sells all over the world, they play this game at a different level. Repair shops don’t even register on their radar.
