Huh?

The contact tracing is 100% Bluetooth.

You post a beacon periodically, other people post beacons, everyone is listening for that UUID and records and instances of it. This is how the whole thing works.

GPS would be a privacy disaster, if it it did work for this. Random rotates beacons are a privacy issue if you don’t trust your phone mfg, which you should not, but as long as it’s an optional thing is O.K. in the way AppleGoogle are proposing.

That's how it can tell you were very close to someone -- all of the other tracking apps do it that way, too.

I'm not familiar with app engineering, but wouldn't the location access be enough for that?

It's not app engineering, it's a comparison of GPS accuracy (especially indoors) vs a bluetooth beacon. Beacons work great no matter where you go.

I'm currently on the 11th floor of a building. GPS accuracy in the vertical dimension is much worse than horizontal. A bluetooth beacon will tell you if I'm in the same room with someone else.