They damn well better. I'm perfectly happy with my board from 2017. Even if it might bottleneck my newer GPU.

Same boat here. My GPU utilization literally hard-caps at 85%, but I've had the same ~$90 mobo for 5 or 6 years now, increased RAM a year later and got the latest available CPU for it last year. When (or "if", looking at where personal computing hardware is going) I do upgrade the mobo/ CPU it'll have the side effect of giving me a 15% bump in GPU performance as well.

AMD is far from some benevolent angel of a company, but between keeping cpu sockets viable for as long as possible, and maintaining open source GPU drivers, they are least keep hope alive that upgradeable PCs aren't completely dead for consumers.

I'm nothing but stoked that my AM4 CPU can still get my GPU to 99% utilization, then. Once I finally jump to ultrawide, I wonder if that will change.

99% / 100% GPU utilization means your GPU is doing everything it can to push frames out. Increasing monitor resolution will not make your GPU work less hard; frames will go down but utilization will stay the same.

Good point.

It's a great move for AMD, not so much for their board partners.

When budgets are stretched, anything that would go towards a new board can be spent instead on a higher tier new CPU.

Engineered obsolescence is rarely a good idea. If the motherboard specs or s9cket don't need to change to support the new chip, keep it. If the only thing motherboard manufacturers have going for them is an artificially required piece of hardware, then they deserve to be outpaced by their competitors.