Resetting Advertising ID on iPad does not work?
https://support.apple.com/en-us/HT205223 explains what is under Apple's control. 


  Ads that are delivered by Apple’s advertising platform may appear in the App Store on iOS, Apple News, and Stocks.


Other websites use a lot of other methods to collect advertising data


  including browser cookies, mobile advertising identifiers as well as other non-cookie technologies *


Although Safari limits tracking by "Intelligent Tracking Prevention", "Fingerprinting defence" etc., it is not fully preventable against the trackers. 

What you can try is to install ad and tracker blockers. You might want to look into their permission to read and transfer content. 

Also, opt-out of Google Adsense can reduce the "Behavioural" Advertising. You'll still see ads, just less relevant. 
https://support.google.com/adsense/answer/142293?hl=en

*From  http://optout.networkadvertising.org/?c=1