@MrPink brought this up in the Telegram chat and a January release might also be to capitalize on Lunar New Year over in China. Kung Fu Panda 3 did a similar thing back in 2016, though local releases might capsize the film's potential anyways. Still this seems like an understandable decision on Sony's end.
IIRC Phantom Thread was also this secretive in terms of title, release, and promo material. I guess that's just the way he rolls and he has the clout to do it.