This is entirely guessing. But if you were drilling a hole to the sewers, both the toilet and the kitchen needed a hole so that could greatly simplify plumbing and construction.
Sounds reasonable ... I've been to some pre-WW2 city houses where the toilet and shower were directly next to the kitchen. Just running one set of pipes sounds like a good explanation for that.
it says in the article above that most werent connected to the sewers
It's still cheaper to dig one cesspit for your villla than two.