I suspect its reliability. having stuff hardwired means its much less likley to be a network problem when something goes wrong.

In my house I had a tesla powerwall installed (yes I know, rich prick alert) the gatway has some shitty wifi that cant be disabled, and kneecaps the range of my house wifi, because it insists on using the same channel.

The back of the house can pick up the AP in the garden, the top front not so much. So a bunch of things are sporadic now.

tldr:

Wifi is fine until its not. Hardwiring for critical path stuff reduces a hard to diagnose mode of failure.