User numbers aren't really falling now (weren't)
If they fall soon it would be probably economic balance issues I guess
For the historical drop/lack of BB catching on. I would say perhaps its not the GE, but the lack of one ( a good one ) and a lack of tactic balances etc. that plays into other realism/counterintuitive issues with how teams are run, training, how the market works etc.
Unfortunately, user numbers are still falling.
I've been tracking World, US, and Utopia user numbers for the past six weeks, and it is interesting to watch the user base drop on Mondays and then slowly climb back up over the week to then drop again on Mondays.
Anyhow, in those six weeks, US is down 7.6%, World is -2.5%, and Utopia is flat.