In real life, just a select few writers fancied name-dropping SFI in the episodes they did, and never in a prominent role - while S31 quickly became a prominent plot point after its introduction in "Inquisition", and sort of became "required writing" for the DS9 writers. I doubt the people who liked SFI as a concept ever stopped liking it, but they just weren't interested in turning it into a plot point.
In in-universe terms, we could argue that S31 was interested in becoming as public as possible, perhaps in order to better hide its true nature (which might have been a supersecret intelligence organization interested in creating fear and confusion, or perhaps a political fringe movement desperate for backing, or just the deranged fantasy of this Sloan character). Certainly S31 made a lot of noise about itself, contacting supposed recruits without first making sure they would remain silent...
Timo Saloniemi
