And effectively KILL volunteer fire departments, which many smaller communities live or die (literally) on.
Thats just a side effect - Sometimes, police and fire unions vote incorrectly and endorse the wrong candidates.
When the wrong candidates are endorsed by local folks who are often considered heroes by the citizens they serve, citizens may feel that it really is okay to vote incorrectly, based on these incorrect endorsements.
Centralizing their unions will serve to iron out these problems.