It's been some time, but as I roughly recall it: - Very few original content on the platform (and a lot of relevant content is already old and exists elsewhere

It's been some time, but as I roughly recall it: - Very few original content on the platform (and a lot of relevant content is already old and exists elsewhere), and trying to get that content on the platform is a huge copyright minefield. - If you as a website owner wanted to allow your users to annotate your content, you had to include their script snippet to the website. I wouldn't be suprised if a brower extension based method would have been better for bootstrapping that side of the business.