76 per cent of US households are using Wi-Fi as the primary broadband connection
No, they are not. No, their PRIMARY connection will be fiber, twisted pair, coax, or 4G Cellular.
The US does not even have 76% takeup of all broadband where it is available, let alone where it is not, and unless the household is on a small rural WISP they probably aren't using WiFi -- and if they are then the WiFi-based WISP doesn't deliver a service level that is compatible with the FCC's current definition of broadband.
Now, of households with broadband it is certainly probable that 76% or greater have WiFi, but even then many serious home users still use an Ethernet connection on their "primary" devices because they know that the more that they offload from WiFi that everything, WiFi connected or not, will run faster and better.