So, 150 Euros for the pleasure to only try out a game that is not even finished yet?
No thank you, would rather wait a year or two for War of Rights, or for the finished product for a smaller price.
The reason the bar is so high for alpha is because they want people who will actually be committed to it. Anyone can throw 10 euros at a game, or 50, to get access to something, then complain it isn't done (no shit) and leave. People who have the money to spend are people who will actually give feedback during alpha and beta and make a better game.
It was the same deal with planetary annihilation, even if the game itself didn't turn out the way people imagined. There's a huge issue in the gaming community with people taking things for granted and expecting a finished, fully polished game which is actually in beta, and not giving any feedback. It's something that Steam's Early Access has perpetuated, by enabling unfinished games to be marketed and sold as if they are finished products. Sure, the extra money goes into making the game better, but they also lose all momentum as people leave the game because they get bored of what is after all an unfinished problem.
At any rate, the bar for beta access is lower, which will be a more finished product anyway. Also Alpha obviously gets you Beta and Final access as well.