Not sure what that’s supposed to mean, Monzo is still a native iOS app, and let’s not get into a pointless discussion about whether certain frameworks or development tools ‘count’ as being a native app.
The reason for the switch to Google Maps in the early days had nothing to do with how the app is developed and everything to do with Google’s restrictive licence conditions. To use the place data from Google for merchant data they had to use Google Maps as well:
I say this as someone who can’t stand how ugly Google Maps is and asked for them to reconsider in that very thread. Would be (pleasantly) surprised if there was any chance of this changing now.