They have to go massively out of their way, spending a lot more more money both in hardware and ongoing processing power costs, to do that kind of tracking which gives far less reliable results, than simply matching the entry in the database of a specific purchase with the person identified by the card that paid that purchase.
Your "argument" is akin to a claim that people shouldn't worry about having a good lock on their door because it's always possible to break the door down with explosives.
"Don't be the low hanging fruit" is a pretty good rule in protecting your things, including protecting your privacy.
But, hey, keep up the good work of giving them all your personal info on a platter so that their ROI of investing in the kind of complex tech needed to do tracking of people like me remains too low to be worth it.