Considering the size of POI on the map, trying to fit all that text on there and have it be readable would be really hard. And in 99% of cases, you don't really need to know what a POI is on your map. If it's something you want to be able to go back to regularly, you can add custom waypoints and name them whatever you want, like thatguybeard said. I do that for mines sometimes, and have done it when using the Vehicle Madness mod to mark certain cars I wanted to come back to and repair once I was able.