Who doesn’t want to promote and advertise how profitable they are to potential shareholders just before an IPO.
They might want to, but it's illegal.
The "quiet period" is a reference to an SEC law that forces any company to be radio silent for a strict 40 day period during the IPO process. Reddit is in that period now and therefore they cannot say a word.
JPMorgan was fined almost a billion dollars for answering questions on a phone call during their quiet period.