I've seen this across quite a few MMOs - people come for the launch experience, leave, and come back once the game has more-or-less found its stride. Finding that stride is imminent for BioWare.
I've just returned as well. Seems to be a similar story in lots of places. Many people coming back to the game individually regardless of the imminent F2P option. Makes me wonder if it's some sort of memetic function. Either way, I have high hopes for the community moving forward.