They have different infrastructure designed based on the intended audience, different legal terms and agreements on their usage, eifferent rate limiting/accountability, and different features based on what Twitch wish to make available to 3rd parties and what use cases they wish to support.
Just because your request wasn’t adopted doesnt mean it’s useless. The vast majority of developers have no issue getting the streamers they work with to go through an OAuth flow, and following the legal agreements. Feature Requests are assessed based partly on the demand for thst feature by devs, and if its in line with the business interests of Twitch. If no one else has the issue you do, and devs/broadcasters/Twitch actually like privacy and restricting data to those who have need and permission, then it’ll likely get less attention than a feature request thats actually needed by the 3rd party dev community.