It's just probably not in their economic interest to release a full alpha.
At the same time, this isn't Blizzard Entertainment, and they don't have the time and resources to devote to such a prolonged and massive undertaking of feedback without any substantial income to offset it.
I must admit in my naivety that I hadn't really thought about the financial implications of extending an alpha from an employee point of view, I think it's because Larian products do not feel like a budget title, even if Kickstarting should easily point out that mistake.
I was also taken aback by the Kickstarter page that had estimated Delivery for Divinity: Original Sin 2 as December 2016 and we're still Alpha testing the first act in November, but I understand this date has now been changed.
I appreciate both of your feedbacks.