The person at a McDonald's drive-thru is an actual employee though, they're paid for all their time on the job, and they can't just refuse to serve a given customer. A Lyft or Uber driver is a contractor, and is legally allowed to refuse any individual ride.
If they couldn't refuse rides, then saying "pay them for all the time they're in the app" makes sense, but that's not the case. Since they can refuse rides, it doesn't make sense to say "you must pay them for all the time they're in the app", especially since a single driver can be active on both Uber and Lyft at the same time.
One could argue that drivers should be turned into part-time or full-time employees, at which point yes they'd have to be paid for their idle time, but that's a different argument.
