MacOS – Why can’t I open Dropbox via Launchpad

The behaviour is intentional, and works much the same within Expose and Mission Control etc.

It's the way out of Launchpad, and if clicking elsewhere other than on an icon doesn't exit you from it, then the only way would be to start a new program or use a keyboard shortcut or mouse gesture.

If you know the gesture or keyboard shortcut that starts it without having to use the dock, then you will likely know how to reverse the action. But for the (possibly majority) users who happily enter it from the Dock icon this could be very confusing and frustrating as the Dock is removed while Launchpad is displayed, depriving the user of the chance to use it. The fact that there is a new icon for it suggests that Apple expect people to learn about the feature, and at least start using it, via the dock.

If you find yourself regularly missing the icons, perhaps you could look into scaling them up, that may be a possibility, they are huge on my 24", but I'm not sure if this is user customisable.

Launchpad Manager will allow you to delete any app from your Launchpad. Just open it, select the app you want to delete and press ⌘⌫.