[dylan604]

Maybe you're confusing who is meant to be making the profit. The people lying to you about receiving relevant, personalized ads are telling the same lie to those buying ads. The ad company tells both sides the lie and their profits are soaring.

[bluGill]

Those buying ads have of ways to track what works. they needed that 200 years ago already and were developing it. (Not all of course, but the big ones)