1. These things happen. Delays exist in all walks of life. They actually aren't hurting anyone but themselves in delaying a game (added costs/resources).
2. They didn't want to say anything until they could be 100% sure so not to annoy people further - understandable.
3. You or nobody else deserves and "explanation". There have likely been many internal struggles and technical issues with this game that majority of the gaming community wouldn't be able to comprehend even if they told you.
If you want to take this line, you have to understand that people are not remotely beholden to Ubisoft. They do not have to check their emotions against what may or may not be happening at Ubisoft before they feel those emotions.
Delays happen. People are disappointed by delays. Pointing out the former doesn't stop the second being true, nor does it make the second unjustified. That's like saying 'People die. Why get upset about it?'. It's nonsense.
I do not
deserve explanation, but Ubisoft do not
deserve consideration as to why their end result is what it is compared to the initial footage and compared to other games.
I only care about the final product I get to play. If it's disappointing, it's disappointing. Whether it's disappointing for understandable business realities or not has no baring on it.
You cannot only afford one group consideration in this, as you are doing. Ubisoft hype and release a product. Based on their hype my excitement level in that product varies, and ultimately if I think the product looks good enough for my time I will buy it. If it turns out not to be, I will be disappointed by it.
No one is beholden to anything other than that. Ubisoft's marketing for this product was good at first, generating lots of interest, and then they made a number of major missteps. They have failed to control the messaging on this new footage. That's all on them. I don't have to give two shits as to why that is.