I think that they want to make it because it really looks cool.
I have a Lionel TMCC version and it looks great at the head of any train. Most people are just drawn to the PRR T-1 because of its looks. I can't think of any other reason to build one versus any other of the already preserved steam locomotives.
I would rather see a GG-1 restored to operating condition before building a brand new T-1. The GG-1 was all PRR and operated for much longer than the T-1. The GG-1 even had a steam boiler for those needing something to fire.
Joe