Yea, but OSM has variable quality by country, and isn’t really a “navigable” map in most places.

You can’t get turn-by-turn directions because they don’t (consistently) have things like lane permeability, turn restrictions, directionality, etc. You can’t get accurate ETAs because they don’t have speed limits or free flow speeds. And traffic data of course. Unless things have changed, routing class and surface type are also unreliable, so a shortest-path graph algo will take you down neighborhood streets or unmaintained roads.

There is a ton of under-the-hood map data, invisible to the end user, that you need to have to be able to deliver a modern phone navigation experience.

Garmin (and other) GPS devices still exist. They're quite nice these days even.

My phone tends to overheat when I stick it under the window to use for directions, so I tend to prefer the dedicated GPS units anyway.

OpenStreetMaps is utterly useless for urban navigation. No connection to the local transit system, no business directory, it's only useful if you have a physical address you want to go to, and personally I never have that information.

MapQuest doesn't have any of this stuff either. Apple Maps is probably the closest, but it falls very far short of what Google Maps can do.