It could be a variety of reasons. Your atty may be flooded. If you have too much liquid in there, it can act as a stopper and reduce vapor. With higher PG juices, you might notice lower vapor. In most cases, the higher VG the higher the vapor level. Also your battery power may make a difference. If you are using a standard 510 batty, the vapor output may be lower. (think about powering a car.. lower horse power.. less 'umph')
Plus.. to be honest.. I've seen some of the vids, and although I know they are vaping, you can make it LOOK like there is more vapor, just by the way you inhale, etc. If you hold in your 'drag' longer, you will get less vapor, amoung other things.
hth!