Firefighters are practically immune from criticism. The job they do is inarguably necessary, it does take great personal risk, their efforts really can’t be corrupted or perverted, the cause they serve is not susceptible to debate. A firefighter who dies on the job was unquestionably doing something anyone can applaud and admire without hesitation or thought required, and there is no way anyone can use that death as a symbol of some other cause that leads to unpleasant disagreements.
We need heroes, and firefighters are about the only folks we can all treat as such with complete confidence.
One big difference is that police and fire are both paramilitary in nature. They have similar rank structures. They salute during ceremonies. They sometimes march (poorly) in uniform. At least in the academy all of them are treated to military type discipline. They borrow a lot of their ceremonial traditions from the military. Your local lifeguard does not.
For the New York Police Department, the coffins of officer’s killed in the line of duty are covered with the green, white and blue NYPD Flag for their funerals, unless the officer has served in the US military, in which case their coffins are covered by the US Flag.
I am 70 years old, and have seen a lot of police, fireman, and military funerals. They always have the flag draped on the casket if the family wants it. There is no fetish, only people paying their respects to those who give their lives for the benefit of others. Sorry you don’t get it. Perhaps some day when you get older the understanding will come.