The thing is, when the GDPR landed, the ad industry obviously had to convince their customers that ads were still viable.
So, even though it sounds completely backwards, they were at the forefront of GDPR consultancy and had their cookie banner implementations ready to boot.

And while I don't think, what they told those companies were complete lies (only because lying in consultancy is illegal), but well, at the very least, I expect them to not have proactively told them that you could also do advertising without tracking, let alone no advertising at all.