The first pass of a counter-attack is usually a choice between finding a teammate's feet and playing into space. The space option wins more often, and the reason is which direction defenders are facing.
The channel is a defensive seam
The space between a center back and the fullback outside him is covered by both and owned by neither. Responsibility there depends on communication, which is slowest during a transition.
A ball played into that seam forces a decision under time pressure. The center back must decide whether to leave his central position, and the fullback whether to abandon the winger.
Whichever decision is made, one of the two areas opens. The pass creates a problem with no clean answer.
Facing the wrong way costs more than pace
At the moment a counter starts, defenders are typically moving toward the opponent's goal or standing still. Turning to run backward takes time and gives up several yards.
A pass to a forward's feet allows those defenders to recover while the ball travels and while the forward controls it. Two separate delays help the defense.
A pass into the channel is attacked by a runner who is already moving in the right direction. There is no control phase during which recovery happens.
Why the receiver runs across rather than straight
Forwards attacking a channel usually run diagonally from inside toward the outside, or the reverse. A diagonal run crosses a defender's field of view and makes tracking harder.
It also keeps the runner onside longer, since the run starts from behind the ball and angles forward. Straight runs from a static central position are the easiest to time offside.
The angle changes what the pass has to do. A diagonal runner can be found with a firm ball into space rather than a threaded pass through defenders.
What the goalkeeper's position adds
A ball into the channel usually ends with the attacker in a wide position and the goalkeeper obliged to choose between the near post and the cutback. Neither is fully coverable.
That is a better final situation than a central attacker shooting from distance against a set goalkeeper. The channel run manufactures a shooting angle from an awkward one.
It also produces the pull-back to arriving midfielders, which is the highest-value pass in transition. The channel is the route to it.
When feet is still correct
If the defense is already deep and the space behind is small, a channel ball simply runs to the goalkeeper. Space that does not exist cannot be attacked.
In that situation the pass to feet holds the ball and lets supporting runners arrive, converting the counter into an attack against a set defense. Recognizing the difference is the skill.
The trigger is the height of the last defender. High line means play behind; deep line means play to feet and wait for numbers.