AllTrails and other apps like it put publically accessible trail/hiking maps into app form and have user reviews and trails rated for their difficulty. And they use GPS for trail navigation to help out inexperienced hikers or mitigate poorly maintained trail markers.

They also charge a subscription fee for features like the ability to download a map and use it while not connected to the internet. "Pay us or you'll get lost in the woods" is profitable, apparently.

Apple might be embedding trail maps into Apple Maps, but this article doesn't explain that.