The problem is the ones with all the data have no real use for it.
Google, Facebook, etc. tell you they have data, sell you the ad, run the ad on their own site, then tell you how well the ad did, but not in absolute terms. All in a black box. They don’t actually have to use their data, as they’re the ones grading their own work, they can just flaunt it to get buyers onboard.
I work in advertising, I know, it’s just that in the industry it’s pretty well known that Google, Facebook etc. hugely overinflate their numbers as they arbitrarily decide that it definitely did have an effect on you to make their systems look better