Currently not every building's WiFi is accessible to you. Second, WiFi only has a limited range. If your house is at the edge of settlement for example and you take a walk in nature (or just the nearest park!), you won't get any WiFi after the first dozen meters. That area may very well be covered by cellular though. Cellular has a much higher range and will still be very important.
I suppose if you're out in the middle of nowhere away from both any building with fiber and any vehicle with Starlink then cellular might be useful, both those are also the kind of places without any cell reception.