Apple - Why can't I hide my active application (e.g., Chrome)?

This is OS X default behavior in every app if you have hidden all other apps before with "Hide Others" or ⌥+⌘+H. In such a case it's not possible to hide the front most app, that's why both options are greyed out/inactive.

Here's a workaround:

If you hold the ⌥-key and click the desktop, your app will hide.

Go to the Chrome to and select "Show All", the option will reappear.