I think it is played on the pipes because:

1. It is such a simple tune, ANYONE can play it on the pipes, the first time you pick up a practice chanter, you can play amazing grace.

2. It's a tune many people can recognize, almost everyone (meaning Americans, to whom this curse almost exclusively applies) knows the words, as opposed to Flowers of the Forest, which is a much more appropriate piobroch air for memorials, and a much more beautiful song.

3. It's in many ways a non-sectarian, or pan-religious song, not tied to a particular creed, as such, not a Catholic, or Orange, or whatever song, just an old style hymn, so somewhat inoffensive to many people trying to decided how to memorialize a diverse group, which is why it has become so popular at US services. It fits many situations, where either the deceased are a group from various religious faiths, or the people gathered to memorialize a deceased member of a group of various faiths, like firefighters or police officers, etc. would not feel uncomfortable or excluded.

that said, I can't stand hearing this song, which is lovely for a choir of voices, played by one or any number of bagpipes. It is wretched. The Royakl Scots Dragoon Guards started it, must have gotten wanted something more popular to play, but it should have been nipped in the bud.