I can’t source the 80% but it’s probably not far off that on iOS these days. Even so, Google Maps still has about 2/3 market share overall. It dominates on Android, and a significant number of iPhone users still use it. However for Apple Maps on iOS if it’s the default, it just has to be good enough and most people will stick with it.
https://www.theguardian.com/technology/2013/nov/26/apple-map...
Apple Maps used on iOS 3x as often as Google Maps, from 2015.
https://9to5mac.com/2015/12/07/apple-maps-usage-numbers/
I can’t source the 80% but it’s probably not far off that on iOS these days. Even so, Google Maps still has about 2/3 market share overall. It dominates on Android, and a significant number of iPhone users still use it. However for Apple Maps on iOS if it’s the default, it just has to be good enough and most people will stick with it.