Why do Apple TV apps become uninstalled?

WIthin the last week, a majority of the apps I installed on both of my Apple TV became uninstalled. It was as simple as going to purchased and reinstalling. However, this shouldn't happen.

Also, regularly I have to re-register installed apps, meaning I have to renter the code and provide either my account login/password e.g. Hulu, or renter my Comcast login/password where Comcast is the content provider.