It would be most likely simpler to make patch for Animated Morrowind than to change all of the robes in Better Robes. As to why the author would deviate from the common standard of how robes are setup...*shrugs* I can speculate, but would be best to hope the author sees this and answers.
Edit: I have looked into this a little bit more....in vanilla morrowind robes are setup in the clothing tab with the following slots: chest, left ankle, right ankle, of those...only chest has an actual body part asigned. Better robes sets up the following slots: chest, right ankle, left ankle left wrist right wrist, of those..only chest has an actual body part assigned. So I think the problem comes from those extra slots being setup in the esp....since they have no actual need to be there..they could most likely be safely removed to get robes to go back to the 'old' behavior.
Edit2: In fact..in GOTY Morrowind...a number of robes only have the chest slot setup......