To verify you could look at the rates of checked bags in cases where passengers don’t pay an extra fee(southwest or passengers with status or other bag check fee waivers) You’ll see a 20-50% increase in people choosing to check.
Over the past 10 or so years, that never happened. Now, I often pack a medium backpack which I can stuff under the seat in front of me, and not have to rely on the over-head bins. We now often travel with a family of five, so in theory it should be even worse. It seems that people, including us, have been conditioned to pack smaller carry-ons.
