Where are you getting your information? There are entire businesses built solely on top of FB/Insta/etc ads. I went 15+ years on the internet without buying anything from an ad, and then in the last 5, I've made at least 5 conscious, purchases from Insta ads. They've become really good in recent years.
When person X buys item Y from company Z, company Z is unlikely to broadcast that fact. Ergo, the 'system' doesn't know that you have now brought item Y and that you no longer have an active interest in purchasing Y.
*Things may have changed in 20 years so the above is just an outdated observation based on a brief stint at a turn of the century B2B marketing start-up.
Or someone goofed and forgot to include the exclude "item purchased" event in the criteria
This may conceivably be because having previously visited a website is a stronger indicator of interest than say, male 18-30 making $XYZ/yr.
It may also be purely coincidental and garbage. You were going to buy anyway/you already bought it.
The truth most often lies somewhere in-between.
The statistic rigor of the people purchasing these ads is not always the highest. The companies offering these solutions typically have very little reason to not sell as many ads as possible, as long as the metrics look good.
In the end consumers are blasted with stalking ads that they don't want and the entire industry is shooting itself in the foot
It's hard to believe the economy is dumping almost 100B/year into a product that doesn't work.
Seing how massively even Google have mistargeted me and lots and lots of others I'm even sure it is a fluke anymore:
AFAIK Google sells ads not by the click anymore but by the impression. Now, how do you maximize revenue? You show the most expensive ad to as many people as possible.
A little (ok, a lot) of fudging here and there and I am a target demographic for shady dating sites / mail order brides / senior dating / gay cruises for 13 consecutive years.
Was it ever relevant to me? No way. I even repeatedly reported those ads.
Does relevant ads exist? As Facebook has proven a few times: yes.
Did Google earn a lot from them? Probably yes.
There are many success stories with ads. I’ve been involved with two exits that is all attributed to digital advertising. No where else do you get a ROAS in the double digits. Here is a good example of the difference. When I worked for a challenger bank. We paid under $75 per signup and $10 per app install. Chase and BOA pays $1200 per new customer in marketing expenses using traditional marketing channels.
Citation needed.
Now why would you go and think a thing like that?