When airlines started charging to check baggage, passengers started carrying more bags into the cabin. That has resulted in:
1) Longer boarding times while passengers struggle to stow their bags.
2) A greater danger to passengers because of the potential of more flying luggage during an emergency maneuver.
3) Less money collected on bag charges for the airlines.
In short, a perfect storm for regulating carry-on bag size that is now a proposal in Congress. Smaller bags are at the top of the flight attendants’ wish list. Currently there are two sizes of carry-on bags: domestic and international. Domestic airlines usually allow a combined measurement of 45 to 55 inches, length x width x depth, while international carriers are more restrictive.
So check before traveling make sure you know the current carry-on rules of your airline and when shopping for luggage consider buying only those pieces designated as international carry-on size.