How would it gather traffic data if they don’t send a few cars down an unpopular path?

If there’s no cars there, there’s no traffic data to collect. If there are already cars there, just use their data. Google doesn’t just use maps to gather it. There’s not much point in sending someone on an arbitrary detour for the hell of it.

Google does seem to often overestimate the practicality of the more rural routes, often pretending you can always stick to the speed limit there when the actual road would not be safe at those speeds. Plus more crossings, bends etc… slowing you down. Or maybe that day Google figured there was a traffic jam on 40.