This thing was so far below the radar, that I had never heard of it until after it hit the bargain bin.
The short answer, I suppose is that they weren't able to get visibility next to Age of Empires.
The "gaming press" hated it.
Multiplayer, I remember being broken, because of language issues, so no word of mouth through lan parties.
To top it all off, some regions came with Starforce.
Still, GSC the developer deserves credit for being willing to take risks.
I find it somewhat ironic that the only video game depiction of the battle of the Alamo I know of is in a game made by Russian developers.
They also managed to pull Stalker out of dev purgatory , and have it not suck.