The "alpha proof of concept" enables a certain amount of sandbox playability that no other game can replicate. Even in short play sessions, I've had an insane amount of fun figuring out if I can do things that simply wouldn't work in other games, and plenty of others on YouTube have done crazier. (A personal favorite was someone boarding an NPC ship.)
I can't speak for everyone else, but I backed an idea. I gave money to someone who wanted to assemble a game with an unprecedented amount of flexibility and realism. Whether or not that actually makes a "good game" in the end. I invested in something I want to see happen. If it does not happen, that will be unfortunate, and I will be sad. But given that what they are trying to do is borderline insane, it will not be totally shocking if they fail.
I can't speak for everyone else, but I backed an idea. I gave money to someone who wanted to assemble a game with an unprecedented amount of flexibility and realism. Whether or not that actually makes a "good game" in the end. I invested in something I want to see happen. If it does not happen, that will be unfortunate, and I will be sad. But given that what they are trying to do is borderline insane, it will not be totally shocking if they fail.