Rumor has it that some people saw the "ads pay for it all" business model and accepted the deal because they wanted the Internet to be sustainable.
I mean, that's a two-sided deal. "You watch ads, you read content". But that deal has been more and more broken by the ad networks and websites; a lot of sites are unnavigable without an adblocker now.
The days of plain text Google AdWords are long, long gone.
If you don't actually buy anything then you're not sponsoring anything.
In fact generating ad views and not purchasing things from them reduces the value of ads to the website.