Trouble is, on many flights, the carry on permitted is greater than the aircraft can hold. Not an issue on some more touristy flights, but on major business routes, people with a laptop bag and a rollaboard use up that space really quickly. Whilst the laptop bags fit under the seats, the rollaboards don't, and on single aisle planes 3 per side, there is no way you can fit those 6 rollaboards in the available overhead space.

I found it worked very efficiently when I flew Lufthansa quite often - your small bag goes on the plane with you, your rollaboard you drop at the bottom of the steps, and it is there again when you deplane. As you all have to get on the same bus, there is a minimal chance of your carry on going walkabout (deliberatly or just because bags look alike). Everyone knows this is the drill, so they have the things they need for the flight in their small bag / in their hand. The trouble with trying to enforce gate checking the rollaboard when people aren't expecting it, is they may have fragile / valuabe things, their medicines, other things needed for their flight etc. in the rollaboard. It would also work better (ie people being more willing), I think, if the bags were returned as you disembark too - rather than go to baggage claim.

One 'strategy' I heard was a conversation between two ladies waiting to board a very full flight. One remarked to the other than both her (pretty large!) carry on bags were bucket style 'totes', with no zipper, so they 'can't make [her] gate check them'!