To put it bluntly: "I'm not buying the game because they didn't show a lot of updates during its alpha stage" - Said no one ever.
You are right. But that means for the final product when the "full" game, final product gets released, people dont care about its alpha or beta when it is already at the final stage. People care about the present. You are correct, I am sure you heard that most people do not buy the game as alpha/beta.