That's just it ..... it's not "just for the sake of it" (though I'm sure you know that already).
It's all about player movement, and finding space. if those in front of the defenders don't do it, or don't do it sufficiently well, then the defenders (not wanting to simply hoof the ball up the wing in the hope we'll retain it) have to pass sideways, or backwards, probing, with the intent of creating an opening.
When done well, it's good to watch ........ and I admit, when done poorly, it can be tedious.
Sometimes, we haven't always done it that well ........ but that doesn't necessarily make it the fault of the defenders.