The only reason I can think of, Tom, is that the Paraklis Service during the Dormition Fast seems to be more of a Greek rather than a Russian practice. I usually go to the local Greek Orthodox Cathedral during the fast to attend one of the Paraklis services there on a Friday evening, and, lo and behold! I am surprised to see quite a few other parishioners from my OCA church there also.
There are a few OCA churches where the Paraklis (Paraklesis) has caught on, however, and they have increased in popularity in some, but not many, OCA parishes. Some of the parishes of the OCA's Albanian Archdiocese especially have *always* had the custom of conducting Paraklesis during the Dormition Lent. And, I assume you know, that the Paraklis Service does not have to be restricted solely to the Fast of the Theotokos.
Btw, I have the "Paraklesis, The Mother of Light" on CD as chanted by Eikona. Excellent!