I dont know why Rheinland is unatractive in general , but I can say why it is unatractive to me.
1- I am terrible at thinking up names, especially german ones.
2- I just hate those stupied "heirr"s and "lad"s. All my characters have a plain neutral accent.
3- There is noone there.
4- I dont find the Rheinland RP that interesting. It needs something like the buccaneers, a pure pirating faction. I bet you will atract people then:P