Some can be rather arrogant and have poor communication skills and some simply don't have the capacity to improve. The level they are at is quite possibly the limit of their skills. At every level there'll be some refs who are very good and some who are borderline for that level, it has always been so.
I think the training and selection procedures are, at least in part, responsible. However, football associations will be under pressure to have people graduate so may not be strict enough in their assessment. One thing I will say is that having a seen a few women referees at various levels their communication is often better than their male counterparts.