Why isn`t JIRA supporting by default the hierarchy "Story-Task-SubTask"?

[Catharina Zorc]

I have in my current project the problem, that I cannot have the hierarchy Story-Task-SubTask. we can only add a SubTask to a story. So we have much Subtasks to one story what makes the whole JIRA confuse, but we also cannot use the burndownchart. So why is "Task" by missing. I had it other projects where it was not missing. 

[Catharina Zorc]

No the issue type is available but I cannot assign it to a story. As a result, all my projects are incredible confusing. I have one story and many subtasks which are not even pictured in the burndownchart. But to complete a whole story in a sprint is in our setting not possible. SO the burndownchart is useless but the team would like to see their progress. And I would like to see a clear structure. First I am totally confused that this is not a possible. Is there any simple way to create an "4th level"?