Ok, but some extra plumbing (and whatever sorts of engineering studies referred to) and electrical work surely can't as expensive as demolishing and rebuilding a whole building.
These seem like extremely solve-able problems.
Now watch the video to find out why you’re wrong
If it was just the plumbing, then maybe. But its not just the plumbing. Its the plumbing, the electrical, the AC/ventilation, fire codes, and so much more.
Not saying it can't ever be done, it really depends on the building. But its not necessarily a good assumption it can be done well in a cost-effective fashion.