I'd argue (and I expect you'd agree) that had the game been designed from a technical point of view correctly and I'd wager this is something to do with the fact this is Bethesda's first Mobile game, that had the correct desicions been made early on (i.e. during design), then it cost very little to get right (bar a tiny bit of RnD perhaps), rather than finding out its a problem a month or two away from release, when its a hell of a lot more costly to fix.
To those non-developers here - think of it this way. You sit down to design a new house, you have two routes, draw a quick sketch, room there, door here, conservatory here. etc.. But you get building quicker. The other route is to design it in more detail, what the pitch of the roof will be, the exact measurements of the walls, what the construction of the walls will be and survey the land to see what's underneath, it costs more than the first option and takes longer before you have something to show for your efforts.
What we have here is an example of the former, they appear to have made quick and fast design decisions (i.e. Door Here, wall there) without actually thinking of the consequences. i.e. 'We'll have lovely 3D rooms that whilst add little to the gameplay, look nice'. Problem is they didn't appreciate perhaps the technical implications of their choices.
So what happened is that a couple of months before the game was complete (or the house was built), they found that the ground under the half the house wasn't stable and liable to shift. To fix it now is a hell of a lot more expensive than it would have been had they done a bit more planning right at the start and found out about the land and simply moved the location of the house before building started.
Whilst a developer the size of Bethesda really shouldn't get caught with their pants down like this, I go back to what i said above, I wonder if they tried too hard to impress graphically with their game and lacked the mobile development experience to know better.
Even at the load screen (the Vault selection screen) its consumed over 160mb of memory, which to me (a professional developer, albeit not a games dev, although I'm dablling!), that suggests like the memory use is heavily graphics related.