Because if it is released in the final third stage, many players who bought the digital version of "The Bus" in Steam in Early Access won't want to re-purchase the product at the increased price.
Am I understanding you right, that this is the scenario, when someone buys The Bus in EA in Steam, but when it's released they want to have the boxed version, so they'd have to buy the box for the full price?
Because they said if you get The Bus in EA at a low price, you will get every stage upgrade for free. So this question/proposal is just about wanting to get EA, but also the boxed version, right?
If that's the case, I guess this person really wants to support TML Studios and could spend the money twice.