In most countries, international arrivals requires a separate stream of passengers, segregated from everyone else in the airport. Passengers arriving from other countries must go through immigration and customs checks before they are allowed to come into contact with others, as "undesirable" passengers might otherwise sneak into the country or pass off prohibited items.
In the United States, US Customs and Border Protection publishes an exhaustive document called the "Airport Technical Design Standard" (I'm not able to find a current copy online) that details the physical requirements for handling inbound international passengers. Everything about the environment must be controlled to CBP's specifications, from the corridors to the access control systems to the security cameras. These rules extend to the gate area, who can access the plane and when, the movement of uncleared passengers and luggage, even the disposal of international garbage (some airports incinerate it on site to comply with CBP requirements). There are special procedures for where international arriving passengers are taken if the terminal must be evacuated, procedures for allowing specially cleared airport and airline staff access to this secure area, etc... Other countries concerned about border security have similar requirements. All of this is to say that countries spend a lot of time and resources thinking about the design of facilities that handle international passengers with security in mind. Any design where passengers mix or take unusual paths would violate the technical standards for the design of these secure areas.
In addition, some airports treat international arrivals (or a subset of international arrivals from some countries) as "unscreened" for security purposes and require that they must go through airport security before allowing them back into the terminal concourse. They may not require the same rescreening for domestic connecting passengers. For example, a passenger arriving at San Francisco from Frankfurt must go through all of US immigration, customs, and TSA security screening before they can board a connecting flight. If this "unscreened" passenger were allowed into contact with passengers from other flights, he could potentially pass off prohibited items before going through screening.
It is, of course, possible that a particular VIP might be escorted by airline staff or immigration officials through a special route or procedure. This would require the approval of the airport's border officials, as it would bypass the normal security measures for arriving international passengers.