The EU laws require the banners to be shown to all EU citizens regardless of the country they're in, right? I think the only way to be absolutely safe is to show cookie banners everywhere.

No, it applies to EU residents, no matter their citizenship.

No it doesn't. It stipulates that the site operators need informed consent to track you using cookies. So what they do is nag you with dark patterns to obtain it, creating an annoying experience.

Developer here. Its much easier and a lazy way to enable for everyone, rather than tracking ips, citizenship and show accordingly. Developers are lazy.

Which Australian sites require cookie opt-ins?

So then why do you think you see them?

*Edit: Sorry if this came off as rude but it was a legitimate question. I honestly cannot think of another plausible reason that would explain the proliferation of the banners.