My wild guess.
1. The EFs 10-20 is selling well in US, bringing a higher margin.
EF M 11-22 will be better in performance, lighter, equally or better in build, and much CHEAPER...
I sold my Sigma 10-20 soon after the 11-22 news release..
2. EF M is selling much better in other part of the world compared to US.
I think this is the crux of it. The 11-22 is the lens that actually interests me for the M line. I'd like to see a size comparison of this lens with M attached, a rebel or xxD with 10-22 attached, and 5D/6D with 17-40 or 16-35 attached. Ultrawide is where it is at for mirrorless -- no autofocus challenges, smaller size due to flange-back and mirror and all that fanciness.
They won't keep it out, they are just using this to drive interest in the M in the USA. Look at how nuts everybody here just went over the $299 sale. I can't wait to buy one of them used for $200 after the M2 or whatever gets dropped, and the 11-22 will be sitting on B&H shelves by then, I'm sure.
Canon 6d, t1i, 24-70/4L, 20/2.8, 28/1.8, 40/2.8, 50/1.8II, 100/2.8 macro, 70-300/4-5.6, g1x, 430exII, 90ex
Elan 7N with 28-105/3.5-4.5II, Rebel G with 35-70/3.5-4.5, A-1 with 28/2.8, 50/1.8, and 135/3.5