I'm still on the fence about de-privatizing spectrum for a variety of reasons. But the biggest elephant in the room whenever discussing spectrum de-privatization is that the FCC earned US$45 billion from wireless carriers last year, and US$19 billion in 2008's auction (http://www.cnet.com/news/fcc-rakes-in-45-billion-from-wirele...). In the grand scheme of the entire US federal budget, I think that's just a drop in the bucket. But it's still money that the federal government looks forward to.
So on the one hand, the FCC wants to play fair for consumers and tax-payers. On the other hand, the FCC can't really restructure an existing industry without biting the hand that literally feeds their existence to the tune of US$2-3 billion per year if you imagine their auction revenue as ratable over the years an auction doesn't take place.