The two reasons for this move are stiff competition by Alder Lake and a marketing stunt. Still, I really hope this happens so AMD can reputably say they indeed in the end kept their promise - and maybe even some customers are going to benefit from this. I would definitely like to know how many people currently use a 300 series motherboard. I guess it's a significant number in the end, though the first generation Ryzens didn't sell as much as the later ones.
It's a big day when someone upgrades from, let's say, R5 1600 to R7 5800X3D on a 300 series board. :O