I think this is the same reason why people preferred a "Call of Duty" over "Return to Castle Wolfenstein: Enemy Territory" when playing a multiplayer FPS. You do not necessarily want to invest a lot of time to enjoy something.

On a personal note, I really enjoyed "Dune 2000" and "Emperor: Battle for Dune" but I have never really been a huge fan of the "Age of Empire" series. Recently I tried "Impossible Creatures" and it was frustrating. I suppose for I am a very casual RTS player. Each to their own.