The reason behind it is the fact that RP's are, unfortunately, the easiest type of server to host, all you need to have is a build and that's it, you don't need to set up a map with events, download add-ons, create a minigame, have some friends to help as admins, create rules, set boundaries, nothing, just load a map and pretend that you're a character, and due to the fact that almost nobody is motivated to make unique servers for Blockland is the reason why the server list is full of RP's, which is sad.