Probably because it is not going that well. TSMC has even said that the ramp will proceed very slowly and they don't really expect much of a ramp until 2014. My guess it that they still are not getting the yields that they want and are still trying to figure it out. Meanwhile, Intel is finishing its 22nm tri-gate ramp and is moving on to 14nm. You can say you have a process but unless you can produce a chip economically using it then it is not much good.
20nm is not easy. Everyone including the Analysts are assuming that 20nm planar is easily doable. TSMC has been at it for the past 4 years, and don't have it done yet. The problem is NO ONE has actually done 20nm before. Intel isn't there to spearhead the breakthru's required for 20nm.