becos the apps u mentioned are not ATV approved.
approved ones appear in TV playstore, will be displayed on homescreen if installed.
quasi approved ones not found in playstore but if u sideload them, they will appear in homescreen.
unapproved ones not found in playstore, can sideload but will not be in homescreen - u need to install "sideload launcher" app from playstore.
this app appears in homescreen, u can enter it to access ALL installed apps.

ATV os is not exactly the same as generic android - more restrictions, security.
some android apps may not work properly in ATV; some will be rejected by TV security.
above applies to all ATV tv's incl sony's and sharp's.