Why is there a hierarchy of seniors and sisters in universities?

Not that there is such a hierarchy. For me, it's more about politeness and emotional intelligence. In our school, there are students' union and general league branch. Usually, they are responsible for all activities. Sometimes it is inevitable that they will meet some people older than us. For the sake of politeness, there may be some benefits in the future, such as doing important things, basically going through them, so there is nothing wrong with politeness, and it can also be used as making friends. Everything depends on your own wishes.