Bluetooth tracking is noisy and a waste of time for external actors because you can't match it other data points.
Now consider the vast number of “smart nodes” out there (eg street lights) that have multi-protocol connectivity built into them. Whoever controls these nodes can simply scan and log every BLE advertisement that is nearby.
I’m not saying that this is the only way that a person can tracked or that this kind of tracking is definitely happening right now, but it’s a very real possibility.