Why use 5Ghz?
Obviously "because it's free" or at least likely to cost some negligible amount (compared to the $86 billion the FCC thinks it's going to get for its next round of spectrum auctions). And they "need" the spectrum. Bugger the current users. They have no ownership "rights". They have no "economic power", or more accurately "regulatory mindshare".
There is a distressing tendency for hard pressed civil servants, who are generally intelligent and well meaning but have insufficient domain knowledge, to need to rely on "industry partners" to help them "think". Anyone who has been on one of the DoT wireless related study groups or the TAG will have seen this in action.
There has to be a real shift in Civil Service recruitment and training to address this. But how it is to be achieved is moot, especially for acquiring comprehensive knowledge without compromising independence. Can't say I am hugely optimistic. Sadly, the way the US equivalent works with its built in political cycles, stands no chance.
It truly is a pity that the US still seems to succeed in styling itself "leaders of the free world", because "free" in this context means allowing big US money to determine what the rest of the world has to put up with.
Hands off our WiFi spectrum.