When I show my ID at the cash register I assume the person working there doesn’t instantaneously memorize all my details and then write down when exactly I was at the shop, along with other details, to use this info later for their own reasons.

Whereas if I upload my ID to a tech company (that potentially answers to both my own government and foreign governments, as well as having its own ad-related agenda) I am a bit less certain about what will happen to this data.