Sports aren't an inherent public concern, but the idea is that there will be a future return.

I don't claim that building a stadium/arena for a professional sports team will generate profit for the city. It's supposed to be an investment. The city foots the bill for the stadium. The team generates revenue over X years to cover the costs, and it also provides jobs for the city's residents. It's an idealistic win-win.

Again - this doesn't always work as intended.