Because eBay doesn't sell an ad-free premium version that removes ads but then still shows me sponsored ads as soon as I click on a listing or a seller's page. Neither does eBay intercept packages after you've made a purchase to drop their own ad flyers inside, or offer a premium tier that does prevent them from inserting an "eBay recommends square space for all your website building needs" flyer, but you end up with a "monkeybusiness78 recommends square space..." flyer in your package anyway