TL;DR: Apple and Amazon have an agreement that Apple can buy all the sponsored product slots when someone searches for an iPhone, iPad, etc.
Samsung and other companies are unhappy that Apple products show up when their products are searched on Amazon, but not the other way around.
Or their whole comment history: https://github.com/search?utf8=%E2%9C%93&q=commenter%3AMikuChan03&type=issues