I wonder what causes these buildings to have such restrictions on plumbing. Maybe it's like elevator shafts where they eventually take up a lot of space if the building is very tall.
It's more an issue of volume. People showing, doing laundry, cooking etc use significantly more water, so the pipes entering and leaving the building need to be sized differently.
Conversely, adding more toilets, for example, may also pose a challenge. My dad helped design the plumbing system for a rebuild of a football stadium. One of the final tests was to have a bunch of volunteers go to every sink, toilet and urinal in the building and turn them on / flush them simultaneously to ensure that water pressure stayed high and the drain pipes didn't back up.
Adding more toilets in a building not meant for them can be a big deal right after lunch / around "busy" times... Some may not be able to flush or overflow if the pipes can't handle the extra activity.
I wonder what causes these buildings to have such restrictions on plumbing. Maybe it's like elevator shafts where they eventually take up a lot of space if the building is very tall.