Why State of Decay 3 is taking so long

It's very simple and obvious, when you look at what information was parsed out when it was first announced. They said there would be a multiplayer function, and I'm going to assume what they were hinting around at was the fact it was going to be a live service game, and with all the negative reactions to that genre -- and the fact Microsoft already has Fallout 76 and Elder Scrolls Online now, as well as EA Play games like Anthem -- they decided to rebuild the game with single player focused gameplay now.

Such a switch in focus would lead to a year added in dev time, minimum.