but you're forgetting an important fact: the planet doesn't own and run the starport, the Imperium does.
Ah, but back in the period Larsen refers to as Ur-Traveller, this was not the case. The starport codes and capabilities pre-date the Imperium and the rest of the official setting by several years. That's at least part of the cause for inconsistency.
Loren Wiseman has said in several places that one of the models for Traveller pre-OTU was the South Pacific in the late 19th and early 20th centuries. Looking at things from that angle can lead to ideas and possible explanations...
John