Because that's not what those pieces were intended for so the artist didn't include one?
Those pieces are intended as large clutter items for construction site scenes, not to be used as tunnel networks, if you start getting creative with models and using them for purposes other than the original intent, then you will come across things like this, the artists can';t think of everything
I'm sure someone could create a piece for you if you need it, i would myself but i'm a bit snowed under at the moment, maybe next week sometime if nobody else has done it for you i'll give it a shot.
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