Hi Seth:
Not all teachers do (nor should) journalize. I think a journal is for those that may benefit from reflecting on past situations, student interactions, or course content, and want a record of their thoughts.
There are different types of journals and various reasons why teachers will use them. It does take a discipline to faithfully comment. But there are other surrogate methods of achieving similar results by various notekeping activities, from simple to extensive.
Regards, Barry