Smoking cessation
While smoking inside toilets is usually forbidden and can potentially be dangerous, it's impossible to tell who is smoking when the doors are entirely closed. Smaller doorways make it easy to identify the perpetrator since the smoke rapidly escapes. As a result, bathroom gates cut from below instil terror in users, causing them to refrain from smoking for fear of being detected.
Allows for privacy
It's tough to tell whether a person using a toilet with a full door is about to have an unpleasant encounter. Outsiders may see the occupant's feet through smaller gates, indicating that the toilet ward is inhabited.