You say "maybe they have a reason for not providing everything" - I cannot think of a reason not to provide me with API access to my own private bookmarks other than "we decided to invest our engineering resources elsewhere".
Which isn't a bad reason! But it's not a good argument for people not to scrape their own data.
Everything Twitter used to and not anymore enable third party profit off “their valuable” data. It’s economically/strategically unsustainable or so they think.
Which isn't a bad reason! But it's not a good argument for people not to scrape their own data.