I don't know about France, but in the US I never use Wifi, since often I have to go through some stupid sign up page to actually use it and my LTE cell data is

I don't know about France, but in the US I never use Wifi, since often I have to go through some stupid sign up page to actually use it and my LTE cell data is usually faster anyway. I might have my Bluetooth on, though. So the number of people running Bluetooth may be higher than those running Wifi. If people only use the Wifi for a function like the guide it might skew results to only use WiFi as well since you'd only be measuring a certain type of user.