Not to get political, but recall since 9/11 it is *very* hard for some nationals to get into the USA.....so that impacts international people attending. Bodybuilding is hugely popular in my region, but so many people who would attend and can easily afford cannot gain access to Vegas.
For most my people to get entry we must pay a fee and undergo a personal interview with the US embassy [which can take months for an appt], have a set amounts of funds, not be in the miltary, have never had any contact with police, sometimes a full medical is required, and the most restrictive rule is we must have held a job with the same company for 2 years prior....so if you recently switched jobs, forget it.
That is just some examples, there are tons of restrictions. In say London, Toronto etc there is easier access for us, so with Vegas, I know they knock out many from dozens of nations from being able to attend. Just my international perspective here...........