Thankfully Apple has decided to do something about that and has since rolled out iTunes web previews for Apple TV apps. This was initially spotted by Slide to Play’s Jeff Scott (via MacRumors) and as you can see in the screenshot above, viewing Apple TV apps on the web is now possible.
That being said, it seems that for now the web preview only applies to apps that are tvOS-only. This means that if the app is only available for the Apple TV, only then can it be previewed on the web. So if an app exists for both iOS/OS X and tvOS, then the tvOS preview will not be shown in the web preview.
We expect that eventually Apple could roll out the feature to cover all apps even if they are a shared platform, but for now they are tvOS-only.