Your comment explains something crucial about targeted advertising that other people often fail to understand. The ad tech companies provide a platform for advertising, but it is up to the user (the advertiser) to configure and use the platform correctly. Often, advertisers may configure their targeting in ways that are suboptimal. Or, their e-commerce platform may not be properly set up to record conversions and associate them with targets. (Depending on the platform, they may not even have that option.)

Poorly configured ad targeting happens just as often as poorly configured firewalls, servers, Wordpress installs, cloud deployments, etc... probably more often since the consequences aren't as dire.

(Not a fan of targeted ads either, but I often see people complaining about post-purchase targeted ads as if this is a universal problem. So much depends on the specific platforms involved, the skill levels and intentions of the many different ad buyers on each platform, and so on. Results will vary.)

The better ad would market the product your friend just bought to you. The privacy concerns are enormous, but regardless, the data is there today and I'd be surprised if it isn't already at work.

Facebook has a "People who liked your page and their friends" audience option for ads.

Another great one is "lookalike audience based on LTV". So you only advertise to people who are like your biggest customers.