There is so much going on during boarding, especially for the infrequent flyers who are boarding in the middle of all the chaos and overhead bin space does not line up - most of them miss those announcements. And not all planes load them in handle or wheel first, for instance in this case it was a E190. MD80s are the same way, so it is pretty confusing. I know it flies in the face of both efficiency and the urge to get moving, but sometimes I think they need to spend a little more time boarding - give boarding groups more time to get their luggage loaded.