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