@edamame Of the many harassment methods (throwing belongings, pushing off stairs, etc) done in manga, most or all of them usually happen anyway so "pushing type harassment" would happen either way.
The question now goes to "Why stairs?".
Stairs are more harmful than no stairs. The time it takes for a person to fall to the ground also allows culprits enough time to 'reasonably escape'. If it was 'staged', it allowed people to think the fake culprit as malevolent instead of accidental push.
It is also less likely to result in murder compared to pushing someone off a skyscraper (assuming that exists in mid-
evil fantasy settings) [spelling wrong on purpose xD]