The organization knows the answer. The reason he hasn’t announced it is by design.
Odds are favorable that the 2021 team will have less talent than we have seen in a while. Brees won’t have the benefit of a dominant defense to help keep us in games and we certainly won’t have as much depth as we have had in recent years. This is going to make it much harder on Brees to help us get another Lombardi. It will likely be a down year and I would rather see him retire this year, after a playoff season than retire after a season where we miss the playoffs.
I also don’t think his body can handle a full season and I don’t think some the players are behind him. It’s just time.

Or you could be as totally wrong about this as your being convinced Michael Thomas would be gone this off-season.