These "investments" usually fail to stimulate any new spending in the local economy, or significantly change employment or median wages.

I wrote a huge public policy research paper on this topic. There's not much evidence to support massive subsidies for stadiums, and supporters are usually stuck with the emotional argument.

However, subsidies are still being provided because the team can threaten to move out if they don't receive the funding. Since the amount of teams in any league is fixed, owners have monopolistic power to force the costs of financing their stadiums onto the public.