Men sitting when they piss makes sense to me. Primarily it's a cleanliness issue, to keep the toilet area sanitary. I always sit, pissing or pooping. Standing while pissing results in side-spray that goes on the rim of the toilet or on the floor around it. With young children around, they touch the toilet rim or their toys get left on the floor around the toilet, and that is really unhealthy. Grandchildren do the same and are vulnerable.
Uncut cocks seem to splatter the most but cut cocks (which mine is) are also at fault when standing. For those of us really well endowed its also prudent to sit back as far as possible on the toilet seat to prevent our cock from dipping into the water.