> Digital systems can confirm flight instruction from ATC with zero radio communication.

Digital comms is available in the US:

* https://www.faa.gov/air_traffic/technology/DataComm

The issue is that the final approach and landing (and taxiing?) environments are probably too dynamic for that: in this particular situation one of the vehicles was responding to an emergency (fire).

In addition to huge planes, there is baggage transportation, passenger buses (to mid-field terminals), fuel pumpers, emergency vehicles, snow plows, deicers, and general maintenance vehicles (clear debris off runways).