@kim_harding
This really feels like a push in the wrong direction. There is limited cabin space. If everyone had a roll-on suitcase, the overhead lockers would be overflowing. Airlines deal with this by collecting overflow and putting them in the hold. This is tricky because things like laptops or other things with large batteries can't be stored in the hold, which causes further delays.
People using the overhead lockers slow down boarding because they stand in the aisle for ages try to fit things in. More people with big hand luggage also takes up more space in airports.
The main reason people prefer flying with hand luggage only is slow baggage unloading. If you're flying to an airport with good baggage handlers, checking your bag is far more convenient. Drop it when you arrive at the airport, pick it up when you walk off. Last time I was at Stansted, I had my bag from baggage claim before everyone on my flight had made it through passport control. On a previous flight, I waited for it for 45 minutes. That was an outlier (the door in the baggage hold was stuck), but it's not unusual for it to take 20 minutes. If airports had an SLA that said all bags must be delivered before the last person from the flight has made it to baggage claim, and airlines were required to include at least a 15 Kg hold bag with tickets, I suspect most people would prefer to check their bags.