Because maps for naval navigation are based on degrees latitude and longitude. So if you travel at sixty nautical miles per hour in latitudinal direction on this globe you will end up one degree further away from where you started. Angles are important in naval applications as well as aeronautical because ships and airplanes can and mostly do travel in straight lines.

One nautical mile is equal to 1.852 km good luck using that kind of number and converting it to meaningful information on the fly.

With digital systems it is of course not as important anymore (also they are using the metric definition and converting it to nautical miles internally) but courses are still plotted by hand on maps (eg. as a backup solution if your digital system goes belly up). Having a measuring system where one unit corresponds to something meaningful with little need to pronounce decimals all of the time seems like a good idea to me.

So for example you can travel 111.12km in latitudinal direction or 60 nautical miles which is equal to one degree latitudinal distance.

60 is properly divisible by 2, 3, 4, 6, 10, 12 and so on so it makes quick mental calculations easier.

The unit just makes sense for the application it is designed for.