Maybe not, but you could be in a bit of a bubble regarding the average website deployment method.
In my experience as a webdev most website are still very much deployed in a way that’s controllable by those who would put up such an alert.
The problem is rather political. Any organization with a website relevant enough to make such a popup worthwhile would never agree to have such a popup alienating its largest share of visitors.
Small independent sites would, but they would be pretty much preaching to the choir.
For large organizations, there are two ways to limit consequences for individual webdevs:
1. Get fingerprints of the browsers of your superiors (or simply use IP addresses), and don't show the popups on those browsers.
2. Let the script be hosted by a central authority (say eff.org), so they can activate it centrally and the popup appears on many websites at the same time, which will make you look less bad.
