It was probably apparent to them that adding the new crypto payments feature would create at least some kind of community pushback.
Waiting until the feature is reasonably complete and can be judged on its merits is good from a business perspective.
It's especially good to have this information while said coin is already publicly traded on some (albeit obscure) exchanges. Because that allows you, as an insider, to slowly accumulate a nicely sized position in that coin while it's still cheap. "MobileCoin" wasn't publicly traded until December of last year, there wasn't even a live blockchain until that month, so if it's true that the first commits in the Signal server repo hinting at the crypto payment plans were created shortly after the repo went silent in April 2020, it is obvious that keeping these commits secret until at least December 2020 was crucial to successfully realize these good personal business perspectives - a.k.a. insider trading, but nobody cares about it if it's crypto.