You are understating how integrated this stuff is. If you make an Intel client motherboard, all you need to add for the network is the phy, jack and some passives.

I haven't really been following intel boards. AM4/AM5 chipsets (and cpus) don't have integrated MACs. I didn't realize intel was putting them in for client parts (Xeon-D had them, but Xeon-D is weird :p)