Well there are probaly several things
1) the cost. The video game industry is in a rut right now, games have become so expensive to make, some cost as much as movies (ie 20-30 million), and no company wants to finiance any game that is to risky or strays away from the norm.
2) Time. There are massive deadlines and pressure on companies now, due to #1, most games only have a year or so to get finished, and the more things like that you've added the longer it takes.
3) Complexity. There have been several RTS games that try and make terrain matter and units react to them, but they've all sucked. AI controls aren't easy either, if you do see anything like that the best you'd get is: If unit a meets unit c have unit a do x. Designers learned that people don't like to know how to program to beable to take advantage or game features (which the AI controls would have to be). Also the more AI features you include the higher the min requirements for the game, which would mean less people could play it and thus buy it.
4) Demand. RTS games just aren't as popular right now as they were a few years ago, they'll come back. Anything that got green lit right now wouldn't have the funds or time to make a good, complex RTS game like you want.