Release dates are indeed set by Hasbro (either as an estimate of when the stock should be here or a set global release date of a major item or wave), but the issue we have here is when dated items are having their release dates pushed back... which means that the supplier (Hasbro) is having trouble getting the stock in time to meet their own release dates.
That's a concern, as there is now a slim possibility that the supplier (Hasbro) is unable to secure stock at all... and the longer it is dragged out with delay updates, the harder it will be for us collectors to track down affordable alternatives from elsewhere before it is too late.