When GDPR was first going through the public circuit I remember reading the proposed laws and being pleasantly surprised to find that they specifically called out and forbade the likely workarounds, including the obnoxious banners we now see everywhere.

I would love to know what happened. Did the laws get "revised" to re-open the loophole? Was superseding legislation passed? Did the courts reject it? Are there enforcement issues?

That sounds like a legal minefield - I would point out that GDPR-style legislation exists because the legislators don't trust the industry to assess what is reasonable. So the industry would be in a position where:

1) They aren't trusted to be reasonable about user consent.

2) They are only to take action when they judge it is reasonable to check user consent.

It'd probably be a very rocky process to nail down what those words like "loophole" and "workaround" mean as the advertisers start abusing prescribed no-banner situations.

TL;DR the enforcement simply lacks manpower, and the most egregious cases go to court which also takes time.