Originally Posted by
ashill
While siankaan1's scenario is likely, I have certainly seen AA require customers to gate check bags when I know that there is space in overhead bins (either because someone has closed a bin that wasn't full, because a rollaboard was put in sideways, or through other inefficient packing). I wouldn't be surprised if the bins could fit 20% more bags than they do when "full". I think it's plausible that more efficient boarding could help.
I think this is probably the right answer. I'm sure we've all seen FAs go around and re-shuffle bags during boarding - moving rollaboards to wheels-first, etc. If everyone boards a section of the plane at the same time, it may be more likely to have a bin closed and "full" that could have been optimized by a professional
