> There's a well known effect in advertising that advertising a product to a person that has already bought that product generally increases their satisfaction with the product and the purchase, and may cause them to recommend the product to others.

Do you have a link for further reading on that? That's fascinating if true.

Could be - but at least for me it feels intrusive and irritating, not any positive feelings really

It's not supposed to feel good. If 9/10 people have a brief negative thought about the advertising experience and nothing else happens, but 1/10 people happen to have their friend on the phone at the time and makes a referral, then overall that is a win for the brand.