Defensive systems are frequently designed to steer the ball towards the touchline. The reason is simple arithmetic: the line does work that would otherwise require an extra player.
A receiver near the line loses half his field
A player receiving in the centre can turn in any direction and has teammates on all sides. Near the touchline, everything on one side is out of play.
That halves both his passing options and his escape routes, and it does so without the defending team committing anyone.
Pressing schemes exploit this by closing the inside passing lanes first, which leaves the wide pass as the only available one.
Pressure can be applied from one side only
Against a player in the middle, a presser must approach cautiously because he can be beaten in either direction.
Against a player pinned wide, the presser approaches from the inside knowing the only escape is backwards or into the line, so he can commit fully.
Full commitment is what turns pressure into turnovers, and it is only safe when the geometry has already removed the alternatives.
The trap needs a second and third player
The wide press works when the full-back steps up to the receiver, the nearest midfielder covers the inside pass, and the centre-back covers the ball played down the line.
Those three roles are what convert a wide area into a trap rather than a simple one-against-one duel.
Where any of them is missing, the receiver escapes and the defending team is now stretched towards one flank with the far side open.
Building teams counter by refusing the invitation
The response is to avoid the wide pass entirely, either by finding a central option through the press or by switching before the block has committed.
This is why possession teams place such value on a midfielder who can receive facing forward under pressure, since he is the only escape from the funnel.
The alternative response is to accept the wide reception but arrive with support, so the pinned player has a short backward option and a forward one down the line.
The same principle applies in the attacking third
Defences protect the centre and concede the flanks for the same reason, since a cross from a wide position is a lower-probability attack than a pass through the middle.
Attacking teams therefore work to enter the penalty area from the half spaces rather than from the touchline, where the angles are more favourable.
Reading a defensive block by which areas it willingly concedes usually tells you more about its intentions than watching where it applies pressure.