Delta started the Basic Economy madness, but Scott Kirby single-handedly made it worse. He designed it to exclude overhead carry-on baggage unless you had the airline’s credit card.
When he jumped ship from American to United he managed to bring that system to both of those airlines. But Delta decided that was too punitive and never matched it.
American has blinked first and effective for flights starting 9/5 they will allow carry-on bags for basic economy fares.
That leaves United as the only network carrier that still restricts carry-on baggage on basic economy fares.
Interestingly, United has the least restrictive basic economy rules when it comes to Transatlantic flights. It’s only a matter of time until they have to cave in on domestic basic economy restrictions.