>>9298293>>9298299The thing is the classic castles aren't based on any specific castle, much like none of the City cars/buildings are based on any specific car/building. Meanwhile a set of the Titanic is specifically of "The Titanic".
Let's look at the recent Hogwarts Express set for an example of what I mean. Here we have a set based on a vehicle that's based on a specific real life steam locomotive (Olton Hall). Sure it resembles the Hogwarts Express, but it's not a very good representation of the Hogwarts Express. And sure, this is acceptable for a $80 set aimed at children, but for a $630+ set that's most likely aimed at the same kind of crowd that buys sets in the Architecture line, they'd much prefer an accurate depiction of the ship rather than a chibi-fied version just so that people could put their Star Wars and Ninjago figures on board.
You have to understand that not everything can be made in minifig scale. Cars Trains and Jets sure, but huge-ass things like Ocean Liners and Bagger 288s are simply too big to feasibly be made into minifig scale sets.