Eat while you sh*t

Fun fact: eating and pooping at the same time is called shredding, as in paper shredding. I'll let your visual imagination work out why.

Eww

Indeed, the previous owners could be a little overweight and have a really slow bowel movement, leading to numbness in the lower limbs as blood circulation was restricted.
Or they used it as a place to change the baby's diapers and not stink up the place.
Or they did their homework in the toilet (I've seen it happen in big families).
Or they shredded.