The problem is trust. I don't want to get into an adversarial relationship with my printer over networking.

I could enable LAN mode and trust the mode does what it says.

I could trust others firmware reverse engineering to verify LAN mode does what it says.

I could isolate it on it's own wifi and I could block it at the home firewall from accessing the internet, to be sure.

But it was easier to simply leave it off my network.

Yeah, fair enough. I have a VLAN with no Internet access for those devices, it's convenient.