Ok, if you were making this show and wanted to keep him on the set, why would you let him know anything about about the real world? They refer to Atlantic City, Mount Rushmore, Fiji, and several other places. So why not make him think that Seahaven is the world? He wouldn't know any better, and he would think there was no place to escape to.
I suppose that the audience would feel it was exceptionally cruel to knowingly teach a child everything incorrectly.
I agree though, if you make him think that the world literally is only Seahaven, then chances are he'd never want to leave. Then again it is human to want to explore new areas.
I would assume that one of the rules in regards to his adoption in the beginning would be that he received a state mandated education. The movie stated that Truman was the first child to be adopted by a corporation so in essence he was an employee and a minor, even child actors have to go to school and since there was a camera on him 24/7 they essentially had to show that he was indeed going to school. Furthermore Truman was in a full class of other child actors who also needed to attend school for extended periods of time causing the need for most likely real teachers teaching a real curriculum including Geography/US/World History. If you go by the reasoning that he was required to go to school and required to be educated then it does in fact make sense. That he would know about the outside world because of education mandated purposes. They probably also didn't reason that at some point he would want to leave his environment and be determined to see past a certain point. When Truman began there was less of a regiment versus the need to tighten controls as he got older. The director became more and more controlling in regards to shaping Truman's environment to suit his own personal desires and needs for entertainment.
Because they wanted to create a world that was just like the real one. If they'd made Truman's reality a separate one, if they'd made him believe that Seahaven was the entire world and it was flat, it wouldn't be quite the same. I mean, if they really wanted to, they could have made Truman world's a space colony or a medieval kingdom, but it might not have the same appeal to viewers.
There were other children there, I assume he went to school. What would happen if one of the other children let it slip about all those places? Plus it would help explain when characters left the show, he'd wonder where they went. This way they could say "Hey I'm moving to Fiji, goodbye" it would be better than little Suzy falling off the planet.
Think of what that would call for. They wouldn't be able to show him hardly any TV or movies, unless they made them themselves, because they'd have to all take place in and star people from Seahaven. Anything that needs to be manufactured, from food to cars and clothes, would need to have a factory/farm (at least a fake one) in Seahaven. You want some wine? We need a vineyard. You want beef? We need cows and land for them to graze on. Etc.
Somebody touched on how hard it would be for other children to hide the existence of the outside world, but I think it would be hard for any of the actors in Seahaven. Any mention of a film/tv show, music, the outside world, geography, politics, history, or whatever, would potentially tip Truman off to the truth. "Pardon my French", what's French? Somebody quotes Star Wars, well Mark Hamill never lived in Seahaven. Oh Hi Truman, what was that song I was whistling? Well it wasn't the Rolling Stones, since Mick Jagger (and the British Invasion, or the British entirely) doesn't exist.
See you guys at the 10 year prison reunion - Ben Richards
Yep the logistics would get complicated real fast.
Also, it would make the show a lot less appealing if Truman was this brainwashed island boy who didn't know anything about the real world outside of his made up island.