What is an “acceptable” reason to be a fan of a team? Because you were born there? Your favorite player is on that team? Their stadium is sponsored by your favorite food? If there was anything that most people agree on, it’s because it’s your “hometown team.”
Then it just comes down to what your definition of “hometown” is.
For actor/improvisor Luka Jones (TBS’s People of Earth), that means rooting for the teams that play in the city you live in, or nearby to where you live. Jones was born near Chicago, so at first he was a Bears fan.