I can understand why you don't show the upcoming subtasks under the main tasks. You can see clearly, that the current task have subtasks. So it's not necessary.

But why don't you show the earliest due date of the subtask insteand of the due date of the maintask? This would allow me to react to due dates of subtasks.

At the moment I only see that a maintask will end tomorrow, but the more important subtask for today is invisible. This will finally result in missing to complete the task and makes a todo list useless...