1. People like business travelers or those with even minimal levels of status/benefits (who don't pay for checked luggage) don't usually preferentially check bags because luggage gets delayed, it's harder to switch flights when there's a weather etc. problem, and they have to wait at the luggage carousel.
2. Hard and hard-ish roll-aboards are a menace. Especially in a world of generally more casual dress, soft-side luggage would make overheads a lot more manageable--understanding that some people really can't use shoulder bags or backpacks.
(Then there's the factor of how much time and space all that also wastes at security checkpoints.)
Checked baggage has the efficiencies of forklifts and trucks and conveyor belts. Just as airlines fixed most of the problems with those systems and got them to be efficient beasts they decided to disincentivize actually using them by charging extra for what is the cheaper cargo space. I wish an airline would have the courage to reverse the fees structure and charge for overhead bin space instead. (But then I also travel with IBS issues and my patience in deplaning has been severely tested enough that I know not everyone shares quite my annoyance at deplaning issues in particular.)
And for the pedantic really small planes like Sansa in Costs Rica for their 30 minute flights between San Jose and other cities.
We hate lugging luggage around the airport for layovers and now that we don’t live in ATL any more, we almost always have layovers.
On vacation I don't have my work laptop, so it's easier to toss toiletries and an emergency change of clothes in a small under-seat carry-on bag. Besides, tourists aren't expected to smell nice and look put-together, and are more likely to have a flexible schedule that would let them go shopping if the bag doesn't turn up.
Only once has the airline lost my bag while on vacation. It was only slightly annoying and they found the bag and got it to me eventually. I've seen a coworker whose bag was lost on a business trip to India. He was stuck wearing the same clothes - a tshirt and jeans - for multiple days. This included time in the office (which had a dress code) and at least one business dinner.
Not that taking everything carryon was really an option in this case, but I had a bag misplaced after a connecting flight was canceled. This was a group hiking trip but I had at least an extra day scheduled. Still spent about $500 to minimally restock although my bag arrived at literally the last minute before one of the guides left the hotel for our one-way walk.
https://en.m.wikipedia.org/wiki/Quepos_La_Managua_Airport#/m...
https://www.vacationscostarica.com/_next/image/?url=https%3A...
But that has more to do with the realities of the plane and the airport infrastructure like you said. It’s not about airline policy with regards to checked bags vs non checked bags.
On that plane, they not only weigh your bags, they weigh the passenger to make sure the plane isn’t over the weight limit.
At Copenhagen Airport, I usually get off the metro, walk to the luggage tag machines at the end of the platform and scan my passport (or boarding pass). That prints a bag tag (and boarding pass if requested), so after sticking that to my luggage I drop it off at the counter — I put the bag on the scale/conveyor, it scans the barcode, prompts me to press "Confirm" that there's no explosives etc, and I'm done.
I scan my boarding pass to go through the barrier into the security screening, walk to the gate, and very often scan the boarding pass again to get onto the jetbridge.
I can easily go from the metro to the plane without interacting with anyone. I understand this is Scandinavian bliss.
(Exceptions are trips to countries where I need my documents to be checked; e.g. to go to the USA a checkin agent has to see my ESTA visa waiver. Oddly, going somewhere like China which requires a printed visa in my passport does work on the machine, as the machine prompts me to scan it.)
I found American airports less hands-off (especially security, which is considerably more hands-on than I'm used to, "Sir, I will now rub your balls"). But then I'm almost always flying internationally out of the USA, so it's not a fair comparison against domestic (Schengen) flights in Europe.
(Delta also has a third type of "gate check" if you count the regular checkin desk silliness to try to skip bag fees by checking in with 0 bags, getting asked if you want to gate check, and then checking it at the checkin desk like checked baggage is supposed to work. That also goes to your final destination, but it's a silly process of "no I don't want to check bags" to say that "yes, I have one bag I would like to check but it's not worth your silly fees to check if you want to charge me".)
I also have met people that like the "jet bridge checked baggage" and think it a feature, not a bug. I understand there is a flexibility it offers if a connection fails or is too delayed or what have you, but the slow, artisanally hand tossed baggage part of that seems so inefficient and slow down to the rest of us, it is hard for me to not see that as a bit selfish and something that should have fees to pay for the extra labor and time involved. Also, if anything it seems a reminder that Baggage Claim got put on the wrong side of Security checkpoints in the US out of a mistake from historic airport layouts, and if you were to design the system from scratch you'd put it before leaving Security and allow people the option to choose which destinations it needs to be picked up (but still defaulting to the final one), and maybe a "recheck" desk right next to it.