~5 floors is as high as you can go before needing an elevator.
At the time the buildings were constructed, 5-6 storeys was a practical limit.
Not just people, but food, water, and waste travelled by stair (or, in the latter case often, air).
What this means in practice is you don't build between 6 and 10 floor buildings because the numbers won't work out. (obviously there are exceptions)