That's always been kind of the thing with D&D. The social and cultural elements have been very streamlined over the years, with the onus being on any given DM to flesh out interesting variations from the norm. Of course, not every DM wants (or should be expected to) put in the work to differentiate the variety of subcultures that would exist within any given group, so the default then becomes the brief descriptions provided by the PHB or MM which does lead to at least some degree of stereotyping.
I had my players run across a Hobgoblin acting troupe once. They had taken to guerilla theatre to address their grievances regarding unjust local employment restrictions. Fortunately, my players had long since learned that not every encounter was meant to be handled at sword point.
