I did not see the connection, but I think private market investors did. They saw that if you could sell web ads (Google) or sell mobile ads (Facebook) at zero marginal cost to each additional advertiser, you'd have a company worth 10x revenue. Investors made that bet and for the most part have all been paid very well.

In my mind the web has always had ads although maybe for a brief period this wasn't true.

The real turnaround that happened around this time and I guess before is that the platforms started realising how valuable user data was and the relative value of "smart" data-driven advertising as compared to "dumb" content- based ads.

Now when I see that a platform has amassed x million users I'm very cynical about their motives for doing so.