I believe they did it because OSM in most places is very outdated or even non existent for businesses, which was probably one of the top uses of it in a search engine.
Having contributed quite a lot to OSM, I can say though that it was generally a lot better for hiking tracks than Google maps.
Agreed. For up-to-date info on businesses I rely on Google Maps, but for hiking it’s totally useless compared to OSM. I still buy some "official" paper maps of the area I hike in because I’ve had bad surprises with OSM, mostly because some mappers sometimes invent some paths based on outdated, blurry aerial imagery, with no real experience of the area. I wish there were a tag like checked_at on paths to mark those that were verified vs. those that were only drawn on Bing Imagery.
Having contributed quite a lot to OSM, I can say though that it was generally a lot better for hiking tracks than Google maps.