First is money. It’s always the money! In many places in the world, airports (and other infrastructure for that matter, or government-owned companies etc.) have been privatized because there wasn’t any money and this was a way of attracting money into the sector. Canada (see relevant articles below) pursued their own spin-off of government-owned airports in the 1990s for this reason (what they did is not privatization, however).
In the United States, till now, lack of access to money is much less of any issue. For most airports, the availability of government funds, fee income, income from concessions, etc. has been enough especially when combined with access to the capital markets, some of which is tax advantaged. Thus, there has been no need to move in this direction to open up a tap of funds. That is not to say the U.S. airport sector has access to all the funds it needs. That’s an on-going discussion. But the same hunger for basic funding that impels many to privatize around the world has not been present in the U.S. This is amplified by the fact that airport managers in the U.S. have become excellent at using whatever it is they have access to in terms of funding. Thus, no one ever throws up his or her hands and says they are out of money.
Second is the fact that U.S. airports are quite competently run. Like any sector, one can point to an exception or two, but overall the sector is quite well run. In some parts of the world, it was felt that privatizing the airport would result in more competent management. This is much less of an issue in the U.S. There does remain the fact that in many cases outmoded public procurement and personnel practices make decisions harder for airport managers, and this is a reason some express interest in privatization. But there is no crisis of competence in U.S. airport management.
Third is a simple general sense, especially among many current airport leaders, that airports are a public good and should be run for the public benefit. Local media and taxpayers tend to think of airports the same way. Airports are NOT seen as businesses by a large majority of the population, the press and political leaders in the United States.
Fourth, the system of public ownership is supported by airlines and by other airport users. You would be surprised at how often airlines and other users complain to airport boards, or city councils or mayors or state legislators or governors about airport matters. You might be even more surprised at how effective they are in doing so. Whether for better or for worse, this is a fact and this makes airlines much less interested in new business models, even if the new model might lead to greater efficiency. (Sometimes such greater efficiency, for example in the use of gates, might not be seen by a particular airline as something to be desired. A business-like approach might be less likely to sign exclusive use agreements, for example, as pointed out by Bob Poole of the Reason Foundation). In most communities, people equate airlines with aviation; they see the airport simply as a facility to be managed. So airline arguments hold a great deal of weight in the current system (and that is why in the pilot program, airlines are given a great deal of say).