And you don't. You can do it for free. DNS is quite effective at blocking ads.
It is amusing to see Google trying to push this "contribution" scheme.
Clearly, ad blocking is sending a loud signal to the websites that "make you the product". Websites that are "free" through advertising sales but also attempt to make a record of everything you do at the computer (and are continually becoming more and more successful at it).
There will always be content on the www. I have watched it grow since its inception and from the beginning quality content was contributed without any expectation of return. Why? I really do not know, but this is how it happened.
And I have no reason to believe www users won't continue that tradition even if ads completely disappeared.
Perhaps this is why sites like Google never try to charge people. Because the www has always had heaps of free content. Maybe these large sites, Facebook included, know that if they were to charge, most people would not pay. There might be a backlash.
It is silly to pay for ads to be removed when they never had to be there to begin with. Yes, I remember using search engines before there were ads. But I know there are generations that never experienced that, and who probably find it hard to imagine.
Ads are smothering the flow of content over the www, not enabling it.