The reason more so from Canada and the US is that most European flights have to overnight in the US increasing cost and reducing amount of vacation time in Belize. Plus for some people they have to get visas for the states and belize again increasing the cost of the trip.
Yes most Canadian and American visitors have to change flights at least once.
But I will tell you it is most frustrating going thru customs in your own country then landing in the states and doing it all again sometimes twice. If we want to increase tourism forget International Arrivals in San Pedro lets just work on getting them to Belize City. Or better yet flights from Cancun or Playa to San Pedro.