I remember searching this out of curiosity a while back.
It has to do with the fact that when immigrants from Ireland and the surrounding areas came to the US, they generally had little money and were highly prejudiced against (No Irish Need Apply). As a result, they were stuck with low wage, dangerous and laborious jobs, such as being a firefighter, police officer, mailman etc...
There was such a high proportion of Irish/Scottish workers that their influence shaped certain traditions, such as the bagpipes at a police funeral.
hi! there's room for more input on this, but FYI, there have been a few similar questions; check these out for previous responses
How did bagpipes and pipe bands become so closely tied in to police departments and fire brigades?
Why do ceremonies for police and fire departments across the US feature Gaelic music and dress?