Have they ? Every major iOS update has major updates to the Maps app.
It is slowly bridging the gap with Google Maps and the issues are still mainly with POIs which Apple arguably can never fix. Unless of course they do their own Street View and invent their own captcha system.
It tries to be too clever, resulting in often frustrating and silly route adjustments
Regardless there are plenty of third parties who are in this space that companies like Apple license their data from. There's no reason someone can't compete with apple on POI quality.
Apple already licenses its data from many providers e.g. Foursquare, Yelp but that only gets you so far. Google is much further ahead largely through their own technology.