Quote: " Why do browsers not do this? Or is this just a google thing? "
My bet is that it is a Google thing. (and other sites too)
They are getting paid for the impressions, and more for the click through.
Showing an ad of something they know you are already interested in gives them a better chance of you clicking through for more revenue for them.
All about marketing, and repetition.
If they drill the image in your brain enough, you will finally justify buying that floor wax.
And if you already bought it, then it won't be long before you search/research something else for a new ad.
Coding things my way since 1981 -- Currently using AppGameKit V2 Tier 1