These limitations are really a byproduct of the deal falling apart between Apple and Google. Apparently, Google wanted access to more user data in exchange for adding turn-by-turn directions to Google Maps. They could not reach a deal, so Apple Maps was hastily created and Google Maps was booted from the default image.
In the end I can understand the limitations on the lock screen because it can be tricky to figure out the right way to give third-party apps special permissions like that. This is not some kind of tacked-on limitation that Apple added, but instead it's something that didn't exist on iOS until Apple added it. Remember that Google Maps, at the time, didn't give turn by turn directions at all never mind on the lock screen. Given how cautious Apple has been with the iOS permissions model (compared to Android, for sure) this shouldn't be even slightly surprising.
The fact that you can't make Google Maps the default handler is stupid, though.
> In the end I can understand the limitations on the lock screen because it can be tricky to figure out the right way to give third-party apps special permissions like that
Interestingly enough, I did some exploring into how Apple was doing this and it seems like there's already an (internal) "API" for bundles of code that work on the home screen and lock screen. Currently it's taken advantage of by apps like Assistant (Siri), ChatKit (I assume this is Quick Reply notifications?), Wallet (which shows up on the lock screen), and the Wi-Fi picker in addition to Maps. Check out /System/Library/SpringBoardPlugins if you're curious.
In the end I can understand the limitations on the lock screen because it can be tricky to figure out the right way to give third-party apps special permissions like that. This is not some kind of tacked-on limitation that Apple added, but instead it's something that didn't exist on iOS until Apple added it. Remember that Google Maps, at the time, didn't give turn by turn directions at all never mind on the lock screen. Given how cautious Apple has been with the iOS permissions model (compared to Android, for sure) this shouldn't be even slightly surprising.
The fact that you can't make Google Maps the default handler is stupid, though.