A personal take is that ad-based businesses exist because there’s no secure widespread reliable approach for micropayments (yet?).
The mean value of adverts on a page is in the order of a tiny fraction of a cent per reader, which is presumably enough for the businesses that continue to exist online. If it was possible to pay this amount directly instead, and have an ad-free experience, I suspect many would do so, as the cumulative amount would usually be negligible. Yet so far, no-one’s figured it out.
(I should mention, there are very strong reasons why it’s difficult to figure out currently, but AIUI these are rooted in the current setup of global payments and risk management by credit card companies.)