[Gigachad]

Every chemistry outputs a different voltage and requires different charge controllers. So sure we could have created a standard lithium size but it would have just locked us in to one chemistry again which will eventually be obsolete. 18650s are also too bulky for most applications. Usually you want flat rectangles. Another benefit of the proprietary batteries is they can completely fill the space available rather than being constrained by the standard.

[samus]

Swappable proprietaries are still better than not swappable at all. For my previous phone I managed to order an external charger and several replacement batteries.