Computers are continually increasing in computing ability, no? 
But unfortunately people pockets aren't increasing with Computers Capability...
Can you imagine the problems online with something like that?? She's already a problem already on MP Servers - and with a full interior?? Take a look at Hudizzles Titanic Model and see how heavy that is - it is an amazing model, but common, it's just not viable to have a full interior for a game, in which V-STEP want to make profit on....you have to bear in mind that V-STEP would actually like people to be able to play the game...
You also need to bear in mind the fact that few people use Titanic, and hardly online at all. Why should V-STEP be spending their time (And money) on a model which probably won't produce anything extra for them? Ie money, for their time and work?
Also - this isn't some "walk around" Simulator, it's Ship Simulator - stuff happens in the engine room and on the bridge, not in the dining room or the 3rd class cabins...Whilst it's alright to have a nice interior to walk around in, i'm sure Captain Smith didn't leave everything unattended to have a nosey around the ship...
If you want to compare it - look at Elbe. How often do you see pictures on this Forum of Elbe's interior? not often...although a Titanic interior may make some Titanic enthusiasts go "wow", it'll make the majority of people go "wow" because of how slow their Computers will be by the time they've finised with it...
Kind Regards,
Jack.