In fairness to their one dimensional tendencies, they are creating and making miniatures for wargames, not miniatures for the Olympics. I think that it is just the nature of the beast that a company like GW is going to product material that is steeped in all kinds of conflict. Surely they are going to focus on one conflict or another, but there are plenty of blocks in the timeline where it is "all quiet on the western front." They probably could elaborate more on the time in between conflicts rather than gloss over it, but that is probably not going to sell any more miniatures.

On a personal note, I have no problem with the Tau in both looks and army play, but that may be because I came into the scene around the 5th edition so they were always part of the system for me. Personally, I would prefer a weird xeno army that just does not fit, than yet another variant of a Space Marine army.