It was by no stretch the first blunder on their side. UBIsoft is already pretty much synonymous with "the company that can't really release anything right". Their reputation among gamers is even worse than EA. And that's quite a feat in some twisted sort of way.
Of course people who enjoy a certain franchise (aka fanboys) will continue to buy their favorite line of games. But only so long. I don't really see much of a preorder potential for the next Sim City game after the blunder with the most recent one. Granted, it was not only a release problem, the game was atrocious too. Way to burn a much beloved title, EA. But I ramble. I cannot really speak for the quality of AC from a gameplay point of view, i.e. whether the game would be a diamond or a turd if it wasn't for the glitches, bugs, crashes and whatnot, because I already dodged that bullet. Mostly due to recent experiences with UBIsoft and not wanting to preorder with them anymore.
I can only imagine that they now noticed a serious dip in preorders, and that's really something studios do NOT enjoy. Preorders are, from a studio's point of view, golden sales. Not only can you 100% predict them (because you already HAVE not only the data but also usually the money), they are essentially a free loan, they are completely independent of eventual reviews (that may or may not be favorable), in other words, preorders are what you want. It's like subscriptions for newspapers, they're also beloved and treasured (and hence usually either discounted or bundled with some nice gifts). Considering what newspapers have to do to sweeten the deal, studios get off VERY cheaply for their preorders. Usually, if you get anything at all, it's some additional graphics to look at or some other stuff that doesn't really cost them a dime, while at the same time people pay (in advance) at least release time prices.
People will only do that, though, if they have a reasonable expectation to get what they want. If you drop the ball once too often (as UBIsoft, IMO, did with AC), people will stop trusting you to deliver. And they will instead only buy after they see some facts that your product is satisfactory, and given the "unbiased" way major reviewers work, today most people will actually wait for reviews from their peers or people they trust before buying a game they aren't so sure about.
And by then not only could they have waited for the price to drop, they could also have seen something else they want and bought that instead!