Paywalls are, of course, the author's choice.
But a paywall is a rather useless page, so it shouldn't be shown in search results. Normally, serving Google one page (e.g. a full article) and showing users something else (e.g. a paywall) would be grounds to ban that site forever, but Google built a special exemption for paywalls.
Showing search results that the user can't actually use is user hostile. It's essentially an ad disguised as a search result, with the problem that those ads displace other results that I might actually be able to read.
Of course, if the policy was to not index paywalled content, we might have avoided the paywallization of the Internet. Somehow, decades ago, when the Internet was smaller and there were fewer eyeballs, high quality content could successfully get monetized with non-tracking ads.
Now we have invasive ads that try to profile you, ads that are full of scams because quality control has gone out the window, and yet, somehow, everything needs to be behind a paywall...