I agree, I cannot think of a great reason to lowering the amount of credits we get per each mini-game, but I do think that the creators and staff members are only doing what they think best for the game, and they know better than I when it comes to that.
However, as mentioned (or hinted at) by players above, there a lot of downsides to lowering the credits. For one, it'll cause a recession. Players' "income," if you will, won't be as high. Just because there are more mini-games does not mean that we will be earning as many credits-per-hour. Plus, I'm pretty sure that people trading rare items will not lower the price of the sprees they want, so trading will slow. If the recession is bad and noticeable, I think it would deter new players who used to trade in the old VMK. In addition, if people earn less, they won't buy rooms or furnishings as often (unless those prices get lowered too, which they might), which would in turn lower the amount and speed of new guest rooms being created, which are a major part of the game.
Eventually, the prices will all even out and the economy will return to a new equilibrium like it is right now, but nobody likes to live through a recession. As mentioned before, maybe they are doing it to counter the high trading prices? I wasn't big on trading in the original VMK so maybe there is rampant inflation and that combined with being more true to the original is why they are doing it?