How does Facebook render our interests and wishlists from other sites and show as advertisements?
Facebook or Google render your likes and interests from the cookies of the website which you browse.
If you might have noticed now majority websites ask for your acceptance for storing information in the form of cookies before you proceed further.
Initially, even WhatsApp was being monitored for developing interests and profiles of people and showing relevant advertisements.
I had read this on Quora earlier, in the case of Google / Facebook their email or social platform is not their products, rather you as a person is their product.
The whole game is about advertising.