Why be quiet if that's the case? What's the endgame for either corporation?
At this time it suits both to officially remain silent about any deal/trade that either has been done, or might be in the works, or might be done later on.
Remember Marvel hasn't announced previous trades or reversions before they were completed and became obvious (DD, Ghost Rider, Punisher etc). The Sony deal with Spider-Man is the only one announced with any fanfare as he is very high profile and the deal itself rather unique.
Even the Ego Trade only came to light from one of Deadpool's screenwriters revealing that in a q&a (afaik other completed trades, if there have been any, do remain a secret). I suspect he might well have been given a telling off for letting that one slip. Note that Gunn certainly wasn't letting that cat out of the bag, though once the moggie was free he had no problem confirming it (too late to deny at that point).
Atm though, the FF is something Fox wont want to be seen as handing back (official line from Kinberg is the film wasn't a 'disaster' and they are still interested in doing a sequel!!), and Marvel would have no intention of fast-tracking a reboot so soon after FFINO anyway.
So it suits both to spin the wheels for a while, let the air clear, then when the time is right let the world know about a deal, if it happens. This is assuming Fox see sense and have/are/will go for a trade while they
can. Better to get something worthwhile to them, rather than lose even more money on another screw up, or get nothing from a time elapsed reversion.
That reversion is the other possibility: Marvel might well have decided to play the waiting game. Let Fox stew on the rights, see if they are dumb enough to try again, and if not the rights would revert around 2022/23 anyway. If that is the end game neither will say anything and we won't know about it until after the reversion.