That would be a compelling argument if the RSS button had never been added to websites in the first place. The UI and UX was left entirely to the website admin

That would be a compelling argument if the RSS button had never been added to websites in the first place. The UI and UX was left entirely to the website administrator, not big tech, and even websites that did not have any monetization did not improve the experience for users. And of course adtech could have invested in RSS to make it financially attractive. But they didn't, cause nobody uses it.