On the bundle download page it says:
Note: We will be updating this page soon, we know it's difficult to navigate so many games. We know you want a button to add show everything in your library. No need to reach out. Any new games added to the bundle will automatically show up here. Thanks!
While not a promise for an add all button, it does seem to imply that such a button is being considered. Absent any other news to the contrary, people will be left wondering what's up with that.