This is unfortunate but let me explain. The Internet world is a very weird place and humans invented this thing called "copyright" - meaning, some thing they own 1s and 0s. We use many videos, images, or audio files from the Internet and we make no profits on the back of them and we credit them all. However these materials are found on all kinds of websites (like Youtube) and these places remove content all the time. To put it simply: when we use a video from Youtube and embed to our books, if that video is not popular or from a known source, it is going to be deleted from Youtube and thus from our book. To avoid this we rarely download some videos that are likely to be removed by Youtube and upload to our Vimeo account. Then embed them to our books. This way we make sure those videos are available for the years to come.
However, in order to avoid them getting deleted from Vimeo or to fill our own Vimeo channel with random videos, we made them "hidden from Vimeo". This means they can only be seen on any other website but not Vimeo. So they are available on tromsite.com or any website that embeds them. We work to fix this by hosting them to our TROMcloud.