I've noticed that too. Maybe the normal Write tool has to output the entire file and this is an attempt to reduce token usage?
But I think it’s mostly a solved problem in frontier models and the bash tool usage is more likely an attempt to be more token efficient - I’ve noticed it used for making mechanical bulk edits that would be numerous “edit” tool uses otherwise
Wouldn't generating a Python script to edit files waste more tokens than using the built-in tool?