I wonder if they have WiFi base stations collecting data at Supercharger points? That's what I'd do.
That would still be only one slice of the many many situations you need to master, and that Waymo already has. E.g. something as simple as entering and exiting a small roundabout, like that YouTube video showed a Tesla couldn't do. Miles driven by Tesla owners aren't purposefully looking for those situations when they engage autopilot.
With how long commutes are in the US, a very very small fraction of miles driven by people on autopilot will be other than "the car was already on the highway, autopilot changed lanes a few times, and after a while was manually disengaged to take an exit".
That small fraction is what could be compared with the miles and number of cars driven by the other companies, because in the latter case it's hired drivers actively looking for conditions of interest to the engineers.
Even if so, uploading gigabytes of data every day is going to be noticed. While I'm sure they have the legal right to do so (via their TOS / EULA) they probably still don't want to emphasize that they're gathering that much data (unless you opt in to their fleet learning stuff).
Generally I think they do to access the Tesla App features. Tesla also have a network connection so they may already be uploading the information anyway over cell networks.
If not, I find it shortsighted and rather cheap that each car doesn't have it's own $50/month data plan (or whatever) to phone home important data.
To have a constant high speed IoT-like connection to the web for real-time updating and such?
I am sure some sort of volume discounts could be negotiated as well.