Hi @azade_bagheri,
It is correct, sub-tasks does not have sprint history when a sprint is activated or completed and inherit that information from the parent issue.
You may look for some custom calculation to get the remaining estimated hours of sub-tasks from issue history on the date when a sprint of a parent issue was activated (yes, it is a bit tangled). Check out this community topic with a similar use case:
Best,
Zane / support@eazyBI.com