Do these notifications actually help with GDPR compliance or are they just a CYA for the websites?
For the common use cases of data by random websites, there really are two common scenarios GDPR-wise:
1) Whatever you're (not) doing with the user data falls under one of the multiple GDPR valid reasons for use that do not require user consent: in this case a clear and informative description in an easily accessible privacy policy is sufficient, and the notification/"agreement" isn't needed for GDPR compliance, the popup is useless.
2) Whatever you want to do with user data requires user consent, but you're not going to get GDPR-valid (informed, specific, freely given and opt-in) consent. There are specific sites that can get meaningful consent because users really want it (e.g. genealogy sites come to mind), but for the random "we want to track you for advertising purposes and share it with 200 third parties", it's not realistic. And the popups don't (can't) help you with that. A popup that allows you to opt out... well, if it's not opt-in, the consent isn't valid in the first place; if the user goes "meh, whatever", then that doesn't count as opt-in consent. If the user is required to "agree" to continue, then that doesn't count as freely given consent. If the user isn't clearly told everything before they intentionally opt-in to every single use case because they want you to do that particular thing, then that doesn't count as specific, informed consent. If you do implement all these things properly, then most users aren't going to opt-in in the "ad-tracking" scenario (which is the GDPR intended result), so companies don't want to implement it properly.
So the nasty popup doesn't really grant you consent anyway (the process is inevitably missing at least one of these key criteria for valid consent), so GDPR-wise it's useless anyway.