Why isn't Motion 5 updating?

Try this. Put the motion app in the trash but don't empty the trash so you can restore it if necessary. Dismount any hard drives that have motion installed such as a clone or time machine. Go to the app store and under purchases tab click on buy. You should not be charged again. There have been numerous glitches experienced with this update, hopefully Apple will get it sorted out.

According to this apple page, it says you should empty the trash:

http://support.apple.com/kb/TS4057?viewlocale=en_US&locale=en_US

The same document has a link with details on how to backup a previous version if you want to keep it.

I'd try one more time using the instructions from the knowledge base, basicly:

-Quit the app store.

-Drag and drop the application from the Application folder to the trash.

-Empty the trash.

-Eject all connected drives, including time machine drives.

-Open the App Store app, and go to the Purchases section.

-Click the "Install" button.