Works when you actually have that option. Usually the only time I ever go to fast food places are late at night when everything else is closed. Most open-late fast food joints in smaller cities and towns will only have the drive through open, not the restaurant area.
In no way does this refute the usefulness of ordering online relative to voice. Maybe those food places don't have online ordering, but that isn't a fundamental limitation.
if you have the computing infrastructure to run AI in the drive through, at night, when everything else is closed, then you probably have the infrastructure to do online orders via an app.
Of course you do - and some do (McDonalds, Chick-fil-A). But not all of them.