The dirt does not go up with the number of bathrooms but rather the number of uses. With more bathrooms you either have to clean less often or less as much.
They don’t get dirty as quickly when they aren’t used as frequently.
Usually in high-bathroom-count houses, there are the “main” bathroom(s) and some bathrooms are mainly just used in the instance that the primary choice is occupied. Like when you really gotta take a leak but people are getting ready in the morning and bathrooms are in high demand.
When visitors are over, the "main" bathroom becomes #1 only, and #2s have to be taken in the less convenient bathrooms.
Like forcing longer-running processes onto a different CPU when congestion occurs.
#1s are usually quicker and more time-sensitive. Nobody wants to piss in the backyard because someone else is pooping. And that has only happened while visiting a 2 bed/1 bath place. Fine for one, but five people overloads the resource, and the scheduler can't pre-empt the running process.
Really, the problem is that the bath or shower and the toilet are in the same room. Occupying the bath or shower should not exclude others from using the toilet. It's bad design that has propagated via real estate marketing.
