There's a difference in being a responsible senior that trains with juniors and draws them along in their wake and a senior that is also an instructor or teacher.
Sometimes it can be complicated though. Many really good instructors I know and some teachers would rather not have the responsibilities inherent in being a teacher. They do it though, to the best of their abilities, because they see it as an obligation they have to their own teachers and their teachers' teachers.
There are lots of good times associated with being an instructor or teacher, such as seeing and taking part in people's growth, etc. However, it is also a huge pain in the butt.
Thankfully, we have people that, for whatever reasons, accept the responsibilities of passing on the art to the best of their abilities. We all owe teachers more than we can ever repay. That's why I am a teacher.