And a huge number of Traveller worlds have population codes between 4 and 7 with tech levels between 7 and 13. Random worlds that Travellers visit will be less populated than midsize cities - the median imperial world population is ~700,000.
Think about in terms of what does that world produce? Not every world is a colony, a lot are going to be commercial concerns shipping some commodity. Thus they will have enough infrastructure to support the production of said commodity and whatever luxuries that the population involved in production require.