"You, as a backer, give money and receive the game as reward"
That's incorrect. What you describe is a pre-order. As a backer, you offer money for the project, which the party organizing the crowdfunding has presented to you. Sure, ideally, you want to see the pitched project become reality and receive the final product - most common motivation for backers is to get their hands on said product. However, being a backer doesn't guarantee that you will get that product, or that it will be in the form that was originally pitched. Depending on the project you might get your money back, you might get some kind of product, you might forget that the project exists, until someone reminds you of it (cough, Mandate, cough). Does Microsoft need money to be able to fund PoE3?
No. If Microsoft doesn't care to produce PoE3, even though they can afford it, do I trust them that they will care, if consumers pour their money into the game even before the project was created?
No. Do I trust Microsoft to keep creative integrity of the project, and put player experience first, before making business decisions, like adding undesirable features, limiting platform on which game will be released, or taking resources away from the niche title if it suits them?
No.
Microsoft is Obsidian's owner and publisher. Their job is to fund and advertise games and profit from their sales. They bought Obsidian, most likely have a power to dictate (or choose not dictate) what Obsidian, can/will do, decide what platforms they will release on, and how their business model will look like, and the OP suggests that consumers should take the responsibility of funding a game for them?
Now, I do hope that the Obsidian's aquisition happened with mutual understanding and that games Obsidian wants to make are games Microsoft wants them to make. I do wish for PoE3 to have place someplace in that understanding. But Obsidian's position has changed, because it is not Obsidian who is calling shots anymore - or in the best case scenario, has a boss which allows them to do as they please, but still has power to change their course if they wish to do so. Trusting folks at Obsidian is just a part of potential crowdfunding - you have to trust Microsoft as well.
Would you crowdfund Disney to produce a movie you like? Or EA? By crowdfunding you don't get rights to the title, nor have real influence on its direction. All you can do is hope that the party you gave your money to will held up its end of the bargain, and that they will be interested in listening to your feedback. And it will be a sad day, indeed, if publishers will start extorting money from consumers, even before the production of the game started.
Didn't that happen with Shenmue III already? "Give us money so Sony will be kind to allow me to work on a game for them?" We will see how this one will turn out.