A multimillion dollar company vs monster truck fans making things in there free time does that.
Problem is Activision is the only company with an interest in making Monster Jam/ Truck games (which are terribly arcadey)
Id love the makers of Motorstorm or MX vs ATV to pick up the Monster Jam video games..
Another un-released game is Monster Truck Destruction, These guys have and are spending so much time with the die hard monster fans to make everything as realistic as possible, I even did some artwork for them. When it arrives it will easily take the cake as the best Monster Truck Sim.
http://www.oddgames.com.au/