Um … they DID. What is happening is with shrinks and efficient pipelines they are bringing more power to smaller packages.
BUT … just like the most powerful laptop lags the most powerful desktop, so does the most powerful tablet lag the laptop, and the smartphone lags the tablet.
Also, the 'core myth' is like the 'megahertz myth' - it was shown last year how many dual-core processors at higher clocks were slower than a single core like in the HTC Titan, and this year we are seeing dual cores faster than quad cores. Also, since Android is the least efficient mobile OS (proven, not opinion - the price of 'options'), and the apps almost universally use battery and processor wasting ads and geo-tracking to sell your info, it NEEDS the power …