Weird. Is that a culvert at the top of the image? It makes sense that runoff from the parking lot would terminate in a drainage ditch, but why it would have sidewalls like that is beyond me. Maybe it was a misunderstanding from the construction crew.
Looks to me like this is a “just get it off the parking lot, we don’t care what happens to it after that” drain.
I bet the pool area was only supposed to have a backstop wall the prevent erosion of the ditch, but the designer didn’t feel like it was necessary to detail it. Seems easy enough to fix with a concrete saw and a sledgehammer though.