My guess is thre previous home owner did the work. I don't think a plumber would do this. Who knows why they lived with it.It would be hard pressed that things are plumbed wrong for a home a few years old where as the previous owners would have had the same complaint. Plumbing wise it looks clean and neat, exhaust is well secured and no signs of condensation. This is leading me that the dip tub has broken off or at the factory it was missed and never installed. Possible it was moved somehow before insulation.