Main reason was they havent been competitive with Toyota, Honda and Nissan. They haven't came up with anything that screams 'I'm unique', I have nothing against the company, my buddy owned 2 Eclipses and now owns a 2009 Lancer. The car is a beast though, it weighs over 3000lbs.
Both are great cars, but have you noticed, you don't see many on the roads and Mitsubishi doesn't make vans. The Colt isn't even in production for the US as a sub-compact car.