Why do Apple pop-up blockers not work on MacOS nor iPadOS?

To clarify, Safari and all web browser that include a setting to block a Pop-Up only prevents the use of the PopUp HTML code to be displayed on a web page. Information on the Pop Up element is here, although the details are not that important.

https://css-tricks.com/newsletter/240-the-popup-element/

Safari is not designed, and never has been, to prevent the use of the Overlay element as it is used extensively on most web pages and blocking the Overlay element would break those pages. The same is true for the other browsers including Chrome and Firefox.

Since Safari does not have a built in Ad Blocker, you would need to download a third party Ad Blocker and they are also available as extensions on other browsers too. They are not 100% effective and in some cases content on the website will be blocked when it should not, but for the most part they will reduce quite a bit of the nonsense ads you will see.

Here is an example where none of these are Pop-ups that would be blocked when disabled in any of the web browsers. These all use the traditional HTML/CSS code used to render a web page and use Javascript to toggle their display on/off. They may look like they would be a Pop-Up and you may even consider them to be a Pop-Up, but technically they are not because they are not using the Pop-Up element in the website code.