GW made the Squats back in 1st edition 40k, then when they were re-writing stuff for 2nd edition none of the designers could face trying to update Squats into a form they didn't find embarrassing, so they let them fade into obscurity for ages then eventually decided to have them nommed by 'nids in the fluff so people would stop bugging them about a codex update.
Because that is always a GREAT thing people do: The second something becomes irrelevant you can immediately kill them off, sometimes in very gruesome and disrespectful ways in order to appease anyone who could have possibly been fans as well as respect the history of the series as a whole.
Looks like GW has learned some lessons from Marvel and DC... Impressive.
But I dunno... couldn't they have done something even more disrespectful at the same time?
Ohh yes! that is right! They created a Tau faction meant to replace them. Which given that they killed off the Squats... yeah
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I am not personally miffed. This is just a REALLY poor attitude for creators to take with their work and I am honestly tired of it in other mediums.
There is a reason why in Strong Bad's Cool Game For Attractive People 3: Dangeresk 3. I actually LOVED the idea of "Retirement Island" a place where sidekicks go where IF you can retire and go there... You are granted immunity to being killed off.
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Another example? One of the creators of Fallout stated that the talking deathclaws in the 2nd game died out completely... Because he didn't like the idea of talking animals. (now THAT cheesed me off... if only because they did so well on them and actually made them imposing and almost mystical as they could see your past crimes)