My theory is that all this is the fault of the cookie law. Before that, the design philosophy was that you could not break the flow of a visitor by pop-ups etc., because they would go somewhere else before even looking at your content.

When all the big websites suddenly implemented increasingly annoying cooking consent dialogs, the flow was already broken everywhere. And so now the floodgates had opened for all kinds "subscribe to our newsletter", "get a welcome 10% rebate" etc., because users no longer has the expectation of an unbroken flow.

And, my god was that law stupid. What we needed was carefully balanced non-negotiable limits on what websites were allowed to do in terms of tracking users; what we got was every website implementing a site-dependent UI for functionality already present in every web browser ("turn off cookies"). The rules got different when GDPR arrived later, both for the better and for the worse. But the flow-breaking pop-ups we will probably never get rid of now that the public has learned to live with them.

End of rant.