Perhaps a cataclysmic event happened that set technology back. Or maybe this civilized galaxy has been thriving for thousands of years before now, and technology has advanced to a very sophisticated grade
I think the civilization in the galaxy started thousands of years before now. This means that there has been a lot of time for technology to advance to where we see it in Star Wars
Because they are from another alien planet who are more ahead of us long before either humans existed on Earth or earth itself was formed...we are just behind which is why our technology isn't advanced than theirs.