system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why American sport teams expect that the public should pay for their stadiums.
gpt
Because they can.

In most instances where a team threatens to leave if the city/state/whatever doesn't build them a new stadium, they get their stadium. 

Lots of people rely on the team for employment, and plenty of others like the team enough that they would hate to see it leave. This results in political pressure to keep the team around.