That's because it's the biggest one, more teeth = wear spread over larger surface area. I think X01 / XX1 cassettes are the most ideal, because they save weight through their actual design, which means only the largest cog has to be alloy. They cost more because they're superior, and the cassette as a whole lasts longer.Meh, I haven't noticed any undue wear on the big alu cog on my XX1/X01 cassettes.
As for the Shimano gear I don't agree, but to each their own and I think it's good to have options. As it stands they are a clear 2nd-place-getter, fine for XT, but not the role of the flagship (XTR) product IMO.