I don't agree much with this assessment.

I voluntarily subscribed some of the Cooper Press weekly newsletters https://cooperpress.com/publications/ They are definitely opt-in, not spam.

I regularly unsubscribe newsletters I didn't opt-in, usually from unknown sources. Not many of them lately and the opt-out usually works. I remember a couple of times I had to send an email with a mention of GDPR in it. It worked.

So "the majority" of newsletters are modern spam, not really.