There are good reasons not to provide line out..
Many broadcasts are in dolby and the external AMP probably has a better decoder for the digital out from the TV
The picture is probably coming from an external source over HDMI and you want the sound to go to the external AMP with the master audio decoder in it
You probably don't need any speakers or analogue sound out from the TV at all (or even a tuner). An AV AMP with HDMI switching is the obvious way to go.