What you're missing is a hidden receptacle behind the TV
Most of these competent installations provide only one in-wall raceway for signal cables - that is true.
However, what is not so apparent is behind the TV is a properly installed AC power receptacle in the wall. This is a standard installation procedure.
Often, the power outlet behind the TV is wired to a power inlet (inverse outlet, has prongs sticking out) near the floor. This is allowed per NEC 400.7. The point of this is to allow the TV outlet to be fed from a power strip, for surge suppression or control.
Many UL-listed "kits" are sold which combine both the outlet/inlet pair, and the large pipe for the user to fit low voltage cables. They are a few inches apart. In North America, anything installed in a wall must be approved by UL, CSA or ETL.
What about all the exceptions I see?
Well, there's no accounting for fools. Lots of people violate Code, and that does not mean it's safe or legal. They'll have problems selling the house and collecting insurance after a fire.
We also have adversary nations shoveling extremely low quality garbage into our markets, that is not UL/CSA/ETL listed. Consumer protection agencies protect our bricks-and-mortar retail channels. But mail order is "the wild west", including mail order that is drop-shipped through domestic warehouses. Amazon Marketplace (3rd party sellers on Amazon) is the poster child for this.