Since MM1 has been in active only few years, because in the next year MM2 was released, a lot of the few MM1 cars makers gone to made cars for the new MM2 game, and a lot of them are US people (this is why there are a lot of US cars for MM1). For MM2 there were and there are a lot of add-ons makers because it's the latest game of the Midtown Madness series for PC. Also the more improved game features made MM2 more interesting for the people. MM3, like now all know, there's only for Xbox.
Now the MM1 players are also very few, imagine the add-ons makers for that game. Have you noticed the poll vote about MM1 in the home page?
![roll :roll:](./images/smilies/icon_rolleyes.gif)
However the story is always the same: nobody will made a car from an user request, especially in this forum. There are some Opel Vectra already for MM2.