A Precarious Situation
Look, it is important to understand the basics of how a house is constructed before putting the blame on anyone. Whoever installed this toilet surely isn’t to blame. You can’t just install a toilet anywhere after a house is built – it has to be in the spot where the proper plumbing was situated.
In this case, it seems the architect chose the top of a stairwell to be the best point for this. Maybe it’s because they were trying to save space. It’s hard to think of anyone doing this without a reasonable excuse. The problem is, we can’t come up with the reasoning behind this. Seems like dismounting will be dangerous.