And get one adapter for each set of headphones. And if you then use those headphones with nay other device and unplug the adapter just hope you don't set it somewhere and forget it.
Ugh, I lose a 1/8" to 1/4" adapter for my headphones at least once a month. I've bought extra and try to keep one in any device I have with a 1/4" port, and yet still they manage to come out and get lost. It's easy and cheap to order a dozen of those. It's not going to be cheap to order a dozen lightning->analog adapters.
That's completely fair. However that's a corner case for most people. I think the general use case is that people have routines in their day to day and fit these devices into their predictable routines.
Adapters suck for unpredictable situations but those aren't common enough and Apple knows this.
Using a pair of headphones with multiple devices? At least between phone and laptop? That's not a corner case, even though Apple seems to think so by skipping out on a Lightning port on the Macs after putting out lightning headphones.
I consider the unpredictable case the several to many years it takes to upgrade all the devices between my wife and me. It probably took 3 years to get rid of all the 30 pin devices in our house. I don't see why it will be any better switching away from 1/8".