The problem is for me, and most of the gamers I know both here in Spain and back in the UK, is we don't have the luxury of having enough space to have a gaming table set up permanently or for long periods of time.
Having limited time means that taking too long to set up the table leads to less time to actually play the game, and more time to clear away.
There isn't really a solution that is going to solve both these issues. You have permanent buildings of a set size, they are going to have a set volume required to store them; and knockdown scenery will not save you any unless you actually take the time to knock it down.
I don't know what it's like in other countries, but I imagine most people living in large European cities live in smallish apartments where space is at a premium, especially if you have kids. I'm guesing that in the US and possibly OZ, more people live out in the suburbs and have more space in their properties.
Guess again. We don't all have three quarters of a million dollars to spend on the project, and may also live in the middle of a city. We may have to rent, or live in apartments or units. Right now, there is actually a crisis of housing where there simply aren't enough to go around, people keep insisting on multiplying and immigrating, and owners keep helping themselves to 25% rises in rent the instant they can legally get away with it.
There is another problem with modular terrain, in that you will pay over 200% of the purchase price just buying MDF flatpacks from some places. You decide you just cannot any more, and it is the same as if the system is discontinued - the stuff you already have is incompatible with anything else. It's hard enough to even sell it, since few people will have a collection of that system, or even that series (eg. they collect Dragonlock dungeons but not sci-fi...)