I figure that they believve that Eldar either have enough attention now, or aren't going to draw many more players so they don't need more work. Idiots in the truest sense of the word.
Why do I get the feeling this holds true? They used to just concentrate on building up and strengthening the already brilliant set of 40k races with each new release of 40k, now though it seems as though they're just pulling in as many different directions as they can. Personally (and I know I'm going to offend a great deal of players here by saying this), I think Dark Eldar were just a mistake. Eldar were cool enough as they were with harlequins, exodites and craftworld eldar. They possessed their own dark secrets and their own shadow-side, they didn't need an entirely new race to better define their darker sides. That and the fact that I just think the models were a rushed job with little real imagination behind them. Sure, they look cruel enough, but if it's sadists you want, what do you think Slanneshi marines were invented for? frying eggs?! I understand that Eldar took a dive into the 'goodguy' realm in the second edition, but GW didn't need to counter this with a 'badguy' army, simply restore the craftworld Eldar's original principles. Why didn't GW simply concentrate on enhancing the craftworld eldar (waveserpents?), rather than launching an entirely new range of Eldar?
As for the other relatively new race, the Tau. I like the models (most of them), and I don't mind their background story, but when you look at a broadside battlesuit, you still can't help feeling sometimes that you're looking at the embodiment of GW's corporate interests...?
Ok, rant over. Feel free to attack my post as you see fit...