Theories why some people haven't got the email:
1. BA are doing a limited trial and you unfortunately weren't selected for it due to some random factor.
2. Overzealous spam filter somewhere along the line which has eaten your email.
3. You've selected not to receive marketing emails from BA.
4. You don't have any F flights booked during the trial period.
Your BAEC status doesn't seem to affect whether you get the email or not. I've dropped down to Blue and I got the email but I had a F flight booked to return me to the UK the other day. I'd hazard a guess and say my CIV is incredibly low so its not that either.