It begs the question why the line doesn't just connect directly to the 2100 South Sugarhouse Streetcar, rather than requiring a transfer at the station. To me, the answer is clear: Different types of trains, so different types of funding, so different projects.
But it raises an interesting point regarding expert knowledge: What is common sense to me is not to my non-expert/non-professional friends and family. But I still need to be able to articulate that understanding, and to do so on a ad-hoc basis: There is no time to prepare a lengthy exposition. I need a ten word 'Elevator Speech'. (And that, I increasingly come to believe, is the essence of expertise: The seemingly effortless performance of public competence.) What will my ten word explanation be? "TRAX trains are too heavy". The issues of rail types, station spacing, double track versus single track, and the engineered weight capacities of different soil types are irrelevant.
Update: Scuttlebutt is that UTA actually plans to use regular TRAX trains along the Sugarhouse 'Streetcar' route.