It is super hard to bootstrap, but sites like Facebook and Twitter already have hundreds of millions of users. Can't they run an experiment - something like "no

It is super hard to bootstrap, but sites like Facebook and Twitter already have hundreds of millions of users. Can't they run an experiment - something like "no ads/tracking for $5 (or whatever amount) per month" and see if there are any takers? If 20M sign up, that is 100M revenue per month. Maybe they considered it and then rejected it as not viable?