I just believe it is a very hard problem. Every country speaks a different language, has different regulations, different shipping companies, etc. It would be extremely hard to operate an EU-wide Amazon, and thus they do not.
I know service workers are used for PWAs and notifications, among other uses.
There's an internal webpage in most browsers that shows you what service workers you have installed (Firefox: "about:serviceworkers"). The answer is a lot, because every web page you visit can install one without your permission. They seem like small javascript applets, and I'm not sure under what conditions they are allowed to run. I am afraid they could be allowed to run even when you are not visiting the page, and since I have no interest in PWAs or notifications I just disabled service workers entirely. You can do that in about:config.
There is no EU-wide Amazon store. There are Amazon stores in some countries, but not all. I think there's no Portuguese Amazon store, which is where the grandparent lives.
>I've been looking for PC parts in the EU and there don't seem to be great choices.
Have you tried online stores in your country? At least in my country many options exist and they have competitive prices. EU-wide ecommerce is a pipe dream