The behavior you describe is expected and intended: A strings.bank file is only generated when you build a master bank.
This is because the strings.bank is meant to be handled in much the same way as your master bank: It contains data that’s relevant to your whole project (i.e.: the GUIDs and paths of every event in your project), not just the content of a specific bank. It’s meant to be loaded when you start your game, and to remain loaded as long as your game is running.