UTA needs to plan for some more light rail. It's like planning for arterials roads--it represents a key link in the transportation network. Think of it this way: Commuter Rail = Highway. Thus, without to connect to, a 'highway to nowhere'? Governance scale also relevant--Commuter rail is the MSA, light rail a County-level project, and street-car a city level project. However, for roads, the Feds pay for most of the highways, the state pays for the major roads (most arterials are 'state highways'), and only the smaller roads are actually handled by cities. On that analogy, there is actually no transit 'small' enough that a city can handle it.
Regardless, Salt Lake County has it's light rail, and Weber, Davis and Utah all have commuter rail now. But UTA wants to build something--they've developed the capacity, and well, 'when you've got a hammer, everything starts looking like a nail'. I'm unpersuaded about the value of streetcars (however awesome Portland's has been), but still devoted to light rail and it's capacity for doing the things a bus can't do.