Supply and Demand, pure and simple.
There is a limited supply and there is a demand for it that exceeds the supply, therefore the prices are high on the MM.
There are many pins that have a smaller supply, but there is not a demand for those pins, so the prices are lower.
Then there is the Addams Family, the most produced pin ever, and the prices for that pin are still relatively high, Why? Same as before, there is more demand for that pin than there is supply, so the price goes up.
It is the same reason that more people collect old Chevys or Fords than collect Edsels, there are more Chevys and Fords than Edsels, but there is no demand for Edsels.
Now, Why is there a demand for the MM pinball machine? I have found that it is a pretty well ballanced machine with a variety of shots and modes. I just happen to like the Monty Python like humor, so the pin works for me. I agree that a lot of the shots are relatively easy, but for us non-pin-pros that helps make the game more enjoyable. I have always walked away from that game thinking, "Gee, that was fun", which I can't say for a lot of pins that I have played. On the other hand, I have played Twilight Zone many times and I could take it or leave it. I just can't seem to get into the game. So it is a lot of personal preference, and it seems that the theme of MM is liked by a lot of people, so the demand is there for the MM.
Flame suit on
Mike