They don’t, but they define the socket the processor slots into and probably did this to market the newer chips as more advanced than they are (by bundling a minor chip upgrade with an additional chipset upgrade that may have more uplift).
I see no other reason to kneecap upgrades like this when upgrading entails the consumer buying more of your product.
That’s exactly what it is. I previously had Intel hardware for a few generations, but I got seriously pissed off that every time I wanted to upgrade, they had come up with a new incompatible socket and discontinued everything older so I had to also buy a new motherboard.
I think they might be a bit better at supporting older sockets these days, but still, too many sockets and incompatible chipsets.
