You could also look at it from their perspective. They did a ton of work before early access and didn't get paid a dime. The early access money is for both the work they already did and for future development. Tons of people have put in 100's of hours into the game and for $20 that's a damn good return on investment. People go to Starbucks and buy a coffee and a danish and spend nearly that and get about 30 minutes out of it.

They took a gamble releasing it to early access. It turned out to be a huge success. If they would have known that they probably could have waited 2 more years, release it much more complete and sold it for $40+. They could also have waited another 2 years and found it to be a complete flop and they earned nothing for 4-5 years of work. Would you do your job for free for 5 years on the HOPE you might get paid or possibly lose everything you have?

As it stands now they will likely make less money in the long run. It was a gamble that could have turned either way. Games fail all the time. We'll see how it turns out. They really don't OWE anyone anything. You bought an unfinished game.. you received an unfinished game that a lot of people really like.