Don’t forget that he can race right across the board in a single move, and he can be especially dangerous if black has left a whole row of squares open.
Here black has just managed to close off the corners on the right of the board, but has left the b-file open over on the left. The white king swoops across and occupies it.
There is now nothing black can do to save the game; the king is unstoppable. Black cannot block him both ways with only one move. White has won this game!