The problem with AI War for most RTS lovers is, that people except reactions. When you play a typical RTS you do something and except to get a result shortly after. In AI War however stuff you do adds up on a bigger scale. Most stuff you do at the beginng affects the late game however you will notice only little of it in the early game. Like capturing planets, it adds Ai progress but most people don't get what Ai progress actually even means. Most of what they understand that a big number is bad but they don't understand WHY the big number is bad and how big exactly the number has to be until it's bad.
This comes with the big number of possibilities the game has. You will have a hard time to learn everything and the problem is the game throws everything at you right at the beginning, there is no "slow progress" like in other RTS games. In other RTS games you have typically a straight-forward research tree and in most games you have a mission based campaogn where most missions introduce a new unit and help ypu to udnerstand the purpose of that unit and how you can use it in your tactics. AI War on the other hand gives you everything it has right when you start a campign and you have to find out all on your own.
When you play RTS on a regular base you EXCEPT that the game feeds you units with a spoon. And not getting fed is what people turns quickly off, stopping right at the start.
Even IF you manage to bear with all this, this ist not a granted victory. You still will take your time until you win the game.
The game is, on a long run, for people that like a challenge AND have the time to learn the mechaincs. I find AI War in this case similiar to Dwarf Fortress. It's a really great game once you learn it, a complex game with a lot of features. But it's also brutal to learn with the most dumbest UI I've ever seen in a game. And no, this has nothing to do with "retro" or "ASCII". I could live with the ASCII graphics if the user interface and the controls where a lot better. I tried DF multiple times but sometimes gave up because the controls are too terrible and you have to scroll through multiple interfaces until you finally find what you want. I know there exist workarounds but let's be honest, a good game shouldn't need any workarounds to be playable and most DF fans use only modded versions of the game because otherwise it would be for them too painful.
AI War is int his way a lot better but it's still not a perfect user interface. This scares people, people nowadays are used to easy understandable gamign where you spend 5 minutes with learning but with a high gaming time (shooter).