Purely from a materials perspective, 2x cheap WiFi-capable microcontrollers (e.g. esp8266) will cost the manufacturer something like $4-$5 total for both devices - which is comparable to 3m cable+connectors+cheap chips to handle the cable connection (even ignoring the cost of some person to install the cable which is far more expensive than that) so indeed I don't get why the author considers that doing the connection over WiFi is somehow wasteful.