Although I am sure it happens, I don't think that passengers with over sized, heavy carry-ons is the main problem. The problem is simple, IMO - they charge to check bags so now everyone takes a carry on.
We are a family of three and I used to pack one large case for check in and one carry on for valuables and meds. Now we pack three carry ons. Multiply that by many, many travelers and you have a whole lot more luggage going into the overhead bins then before. Mine are not over sized or overstuffed, in fact there is plenty of room for souvenirs on the return trip. I actually prefer to travel that way now. Makes getting in and out of airports a breeze.
We are a family of three and I used to pack one large case for check in and one carry on for valuables and meds. Now we pack three carry ons. Multiply that by many, many travelers and you have a whole lot more luggage going into the overhead bins then before. Mine are not over sized or overstuffed, in fact there is plenty of room for souvenirs on the return trip. I actually prefer to travel that way now. Makes getting in and out of airports a breeze.