Well, two things standing in the way are money and expertise. Running a real root server, as opposed to a toy one that only you and your twelve best friends use, is a a significant operational challenge. I gather a typical root costs about a million bucks a year.
The other reason that nobody sets up new roots is that there is no actual reason to do so. For all that ICANN does a lousy job, the roots work fine and nobody other than a few get rich quick artists and foolish idealists want root domains other than the ones there already.
Of the new domains that have entered the roots in the past few years, the only ones with enough registrations to be a financial success are ..INFO and .BIZ, cynical clones of .COM used almost entirely by people whose information you don't want and with whom you do not want to do business. The .NAME domain, intended for personal domains, has a modest number of registrants, largely in Europe, but I see them loosening up their registration rules which tells me that they're scrambling for registration dollars. The rest, .MUSEUM, .AERO, .COOP, and .PRO are failures used by almost nobody. The three new ones ..JOBS, .TRAVEL, and .MOBI haven't been around long enough to fail, but there's no reason to expect them to be any different.
R's,
John