With the TA being free to play, something strongly advertising the fact that the TA is free, trainers are waiting to help with all their needs, the combat and flight modes are easier and friendlier on all the pages leading up to making the two week account may solve this. Right now all the advertising and visuals click guide them to the MA off the bat which may be part of what keeps the roster low. Take a lesson from Facebook on how to steer(coerce) them where the end result will get the better long term results.
The Trainers are a boat load of fun to fly around and furball with for hours in the TA. They work very hard at presenting the TA with that image. Seems that is one of the best kept secrets about Aces High.