Because I as an user would be glad to have "free sites only" filter, and then just steal content :))
But it's an interesting idea and thought experiment.
These AI web crawlers (Google, Perplexity, etc) are self-cannibalizing robots. They eat the goose that laid the golden egg for breakfast, and lose money doing it most of the time.
If something isn't done to incentivize content creators again eventually there will be only walled-gardens and obsolete content left for the cannibals.
While I don’t blame creators for using ads now, I don’t think they’re a long-term solution. Ads are already blocked when people visit the site with ad blockers, which are becoming more popular. Obvious sponsored content may be blocked with the ads, and non-obvious sponsored content turns these “creators” into “shills” who are inauthentic and untrustworthy. Even without Google summaries, ad revenue may decrease over time as advertisers realize they aren’t effective or want more profit; even if it doesn’t, it’s my personal opinion that society should decrease the overall amount of ads.
Not everyone creates only for money, the best only create for enough money to sustain themselves. A long-term solution is to expand art funding (e.g. creators apply for grants with their ideas and, if accepted, get paid a fixed rate to execute them) or UBI. Then media can be redistributed, remixed, etc. without impacting creators’ finances.
If only the one in ten thousand with something to share are left standing to share it, no manufactured content, that's a fine thing.