Because there isn’t a flash port for iOS. There was, at one point in time, an app called frash but it hasn’t been updated in awhile and wasn’t for the Apple TV only iPad/iPhone/iPod.
Unsure, are you using the Media Player or Plex for this?
Are you using the Media Player or Plex? The subtitles have to be enabled in the settings for the Media Player (unsure about Plex don’t have an OSX computer).
XBMC is easy to install. You can install plugins for XBMC as they work on all platforms that XBMC runs on.
In the setup menu, there is a point to set “Sete Indikationer” - That’s in Danish and means something like recently watched abd it’s set to off but it’s still visible