startrekds9:

The Trill taboo against “reassociation” was something cocreator Michael Piller had suggested early on in the series. “He felt they’d have to have a very strict taboo in order to avoid an aristocracy of the joined,” says (René) Echevarria. “Otherwise, they’d all only want to hang out with each other, their dear old friends from five hundred years ago, and it would become a really screwed-up society.”

[Star Trek Deep Space Nine Companion]