Yep, I'm aware of this, when I discovered how the Fantastic Arcade Bundle was done (as a single page) it was too late for them to change it or for us to modify the app to accommodate for that :(
Installing multiple "items" per "itch.io page" could become a feature of the app at some point, but it's not planned in the immediate future (we're in the process of making significant architecture changes to provide more reliable downloads, especially for larger games).
In the meantime, you can still download and use all games individually from the website - I know it's not as convenient as with the app, but at least there's a way to do it! Thanks for your understanding :)