They shouldn't. That's just being stubborn. One, people need to understand that a date on a Kickstarter isn't some concrete release date. It's an informed hope. The games are usually in pre-alpha or alpha. No developer can predict with any certainty the month their game is coming out when they've barely even started making the game. They only can estimate how long it might take
It's like writing a first draft of your first chapter, and then someone asking you what month the book is being published.
And two, those dates are estimated before funds are collected, before stretch goals are reached, before scope is expanded. Context matters. As soon as a project clears a lot of stretch goals or is funded well beyond its initial goal, you should probably assume that date on the KS page is now outdated and not very accurate.
There are methodologies for keeping software scope and planning under control even within an ever-changing context, just like there are writers who consistently deliver books on time (one of my favourite authors, Pratchett, consistently released two books per year until sickness prevented him to, and those were good books). All of these are the excuses a dev would use in the case of a death march anti-pattern. And naturally I'm not saying that this project is a death march, but it's natural that people are gonna be worried because it looks like one.
Finishing projects on schedule is a skill that can be learned, in spite of everything. It's a pity it isn't taught much.
most games are really bad until a point late in development
i don't have a dog in this fight but it's completely unsurprising that what they've released so far isn't fun to play
There are plenty of devs who get the tech and fun right building a prototype with fighting teapots or cubes first, before building the assets on it. One early access game I bought, kerbal, had tons of fun in four years ago already, even though it looked considerably uglier than it does now. But here it happened the other way round, we started with hangars in which you could look at assets without knowing whether the gameplay would be fun. It is a matter of priorities and contributed to long-lasting issues, like adapting cryengine to space-based networked gameplay, which should've been the first thing done since it's the core of what the game's supposed to do. But instead we've got a janky PTU that's sending way too much stuff through the network.
It's probably partly due to the funding model, though, since it's largely based on buying neat looking assets, so they need them to be in-engine sooner than the gameplay.