Reynard
Emperor Mongoose
If only for OTU, every empire except the vargr, for obvious reasons, has a centralized primary interstellar trade network within their borders. The game system is designed for this. Independent and neutral systems need a bit of imaginative thinking as to why they have the 'starport' they do. The local system government or business group have the tech level and resources to build one? A foreign source needs to establish such a trade center and bought the rights? Built during a time of greater power, local or foreign and now inherited?
Reading T5 and other Traveller sources, spaceports are meant to primarily service the local system's immediate needs which can include starship presence but is not the main source of trade which is part of the 'homeworld' designation.
A variant from the Traveller 1e system generation I like is using population to determine starport type, 2d6-7 + population. Makes a little more sense. T5 has highports for each type of starport based on population levels. Reduces super advanced Class A ports with highports on barren rocks.
Reading T5 and other Traveller sources, spaceports are meant to primarily service the local system's immediate needs which can include starship presence but is not the main source of trade which is part of the 'homeworld' designation.
A variant from the Traveller 1e system generation I like is using population to determine starport type, 2d6-7 + population. Makes a little more sense. T5 has highports for each type of starport based on population levels. Reduces super advanced Class A ports with highports on barren rocks.