Because the sites that have set up the paywall will report the extension and get it taken down, happened to an extension that I made a while back that had a similar idea.
https://greasyfork.org/ - it's been a year or so since I've made use of it but after userscripts.org became unusable this was my replacement. they made some sensible decisions about what's acceptable in a script and whitelisted external libraries: https://greasyfork.org/en/help/code-rules
A Paywall Extension, hmmm? What if it were part of a dev tool bundle?
It's arguably unfair that users of Facebook and Twitter and other social media sites should have access to more content than someone who has decided not to use those platforms.