I wonder two possibilities:
1. Apple is going to surprise us with genmoji in 18.1 instead of 18.2. The UI elements already seem to be in place so maybe this will help spur iPhone 16 sales. The betas that have been released this week are all the non- AI ones as some else pointed out earlier in the thread.
2. The new October products will be a press release rather than an event (unlikely I know, but still...) and they are preparing the RC instead with all the goodies for the new machines for announcement next week. After all, gotta boost those sales numbers for the usually best quarter of the year and if iPhones sales aren't cutting it then the sooner the Macs come out the better the sales numbers will be...
However, I suspect there are just some troubling issues that they are trying to nail down and they want to avoid bad press even on the betas.