I'm super confused. In EU all airlines use sizers before the gate, if whatever you want to bring on board doesn't fit into the sizer(and the bag you posted definitely wouldn't) it has to be checked in at a heavy fee. Do US airlines just don't care what you bring in board with you?
The size matters in the US, too, but that doesn't stop a dozen people from trying to get away with carrying on an oversized bag. You'll usually find anywhere from a few to a dozen bags confiscated on the boarding bridge.
