A few examples of why it was so great:
Simple, non social bookmarks. As in: place a bookmark so you don't get lost while hiking, or when you find a nice spot you want to come back to later. Yep, a utility feature that doesn't somehow map to some stoopid business OKR in advertising. I am sure this is possible with Google maps or Apple maps somehow, but only after you've created an account, logged in, and made sure you have the equivalent of a South Korean inner city internet connection.
Also, easily downloadable maps that just stay on your phone. I am hiking, I don't have internet and need the map on my phone. I know Google Maps allows you to do that but it is tedious unlike maps.me, which is instant.