They've stated the reason: Vegas is the only true 24/7 city in the US.
Why can't they just move these conferences out of the US? Dmitry Sklyarov was arrested at one of these Vegas hacker conventions, in case people have forgotten after all these years. There are many other countries where these conferences could be held, and where all this security BS isn't much of a factor.
You mention Dmitry Sklyarov but more recently Marcus Hutchins (MalwareTech) has been also arrested by the FBI following its appearance at Blackhat or Defcon
If you're going to make such a wild statement where the laws are against you any any Google search of hours is against you, you've got to give a much longer and in depth explanation.