Wifi and Bluetooth were evaluated for mice and keyboards by companies like Logitech and Microsoft back around 2000. Back then, Bluetooth was the clear winner. Back then, Wifi chips were very power hungry, more costly, and physically larger, all of which were detrimental to creating battery operated, inexpensive, small devices. Wifi was years away from being practical for mice and keyboards. On top of all this, Bluetooth was better at latency (bandwidth is almost irrelevent to mice and keyboards). Back then, even though Sun Microsystems had produced a wired Ethernet mouse, there were jokes that a Wifi mouse would have to deal with DoS attacks.
This is why they (plus a few other companies) formed the Bluetooth HID work group in the Bluetooth SIG.
As always, technology moves forward and it looks like Wifi has (possibly) become practical for mice and keyboards. It will be interesting to hear about how well (or not) this mouse actually works once it is customers' hands.