Another question of mine (How big is the space faring population in Star Wars?) was duped to a question that cited (presumably canon) information that the galaxy indeed has 100 quadrillion sentient beings on 50 million populated worlds.
So this begs the question: Why, in the movies, not only is this seldom shown (perhaps the map in the archive counts), but (in my opinion) often contradicted?
Three people meeting randomly (Luke, Han, Leia) tend to mention names of planets and react to a name they don't know as it's expected that the other knows it. So shall we believe that at least a smuggler and a princess know 50 million systems and/or planets by name?
I never heard about some ancient race that brought technology to all the other races. So how could it be that everybody knows how to operate technologies on every planet? Why is Leia able to assist in repairing something on the Millennium Falcon (that seems to be gathered together from different places). Why is Luke able to fly an X-Wing with his T-16 (or whatever) Speeder experience? Shouldn't there be millions of different technologies around there and you could be very very happy to find spare parts for a ship if its origin is on the other end of the galaxy?
How could there be famous ships and persons that everybody has to know? Out of 100 quadrillion sentients, are there really just a small number of famous ones who in turn are known to all the other 100 quadrillion sentients?
Last but not least, are the events of our beloved Star Wars storyline really important to 100 quadrillion sentients on 50 million populated worlds? Are all of them suffering from the Empire (or even know about it) and freed by the handful of rebels we know about and having parties at the end of ROTJ?
If the galaxy is really so big, the only explanation for the knowledge (and expectations) of our heroes is, that there is an elite subset of planets (and people) we are dealing with and that the other 50 million do not bother (then why have them?)
So why (if the galaxy is so big) is this seldom (if ever) shown in the movies, and, on the contrary, it seems more to be portrayed as a place where it is possible for a single person is able to know a large amount of it?