Perhaps no need, but what about interest? I have no need to see the Pyramids, but I sure hope to one day.
It sounds like the consensus is the math of the basic books makes it such that the average 3Ier not only has never been off-system, but they don't even know anyone who has. That's sort of bleak.
No, it's sort of realistic for non-American and non-Europeans. In general, the larger the country, the fewer the people (as a percentage) who've ever left it. I've been outside the US a few times, but I've several friends who've never left Alaska, and one who, at 50, had never even left the Borough of Anchorage. Not even so far as the state fair in Palmer.
Most people never go more than 100 miles from the place of their birth. Currently, most Europeans travel at least occasionally within Europe, but during the cold war, the East was mostly people who didn't travel anywhere, no matter how much they want to.
The average imperial citizen in the Marches (for which hard canonical data is obtainable) is from a highly oppressive government with high to extreme law - rigid controls of civilian movement. They are quite likely told nothing about the imperium, other than the relative immorality of the offworlders (many of the high pop worlds are religious dictatorships).
The Imperium IS a bleak place. PC's are the bright spots. Just look at the early canon adventures. The Imperium is a reflection of the Empire of Star Wars as much as it is of Niven and Pournelle's Co-dominion (also not a terribly happy place). It's ugly, racist, brutal, efficient, and makes a pretense at trade. And that's the nice side of it.
The BS addage of "Men, Not Laws" is, if in any way based upon the "reality" of the 3I, a sure sign of abuse, not responsiveness. Think of the likes of Tarkin, quietly seeing to it superiors have accidents and incidents until they come to power. People willing to use fear to their advantage.
Trade isn't the lifeblood - it's the illusion of freedom that is maintained.
ANd the prices of passage are several years income worth for the average man... a price that just doesn't get paid. Even low passage is several months worth, and potentially lethal to the passenger.