They already made 2.2 million dollars on kickstarter, more than their ultimate stretch goal, THEY HAVE ENOUGH loving MONEY!
It's not just about getting more money. Honestly! Did you even read the last few posts!?
There's also the risk that the people buying it aren't going to actually help the development and contribute, which is the entire reason there even IS early access.
They want feedback and developmental support for committed gamers. (Make the game less available by having a closed alpha/beta or by charging more)
There is absolutely no possible way to excuse how the steam players have to pay the same overpriced $90
They don't you moron! The game isn't properly out yet! Take it like this: imagine if they didn't do Steam Early Access but otherwise it was the same situation. It wouldn't be out at all with no price, and it would be unfinished. You'd only get it when it was finished at a lower price, which is what you personally want. This is basically what is happening, it's just if you really want to test the game out and help the development then you can pay extra and help out, otherwise you wait till the game is actually released for a lower price.