I guess they could have added the RPi WiFi chip for about USD 1.5 in BOM cost (assuming common industry prices based on distributor price/quantity matrix)
It would probably make more sense to add an ESP32 rather than a BCM4335 like on the RPi since that chip is intended to run with a full host OS and needs a large binary driver blob (yes the ESP32 also has a binary blob).
Either way it's no longer cost effective.