Why we cannot call future method from batch class as we can do from Queable class in Salesforce?

Hi,

You cannot call another future method from a future method. As per Salesforce documentation,
You cannot call a method annotated with future from a method that also has the future annotation. Nor can you call a trigger from an annotated method that calls another annotated method.
If you do not have dependency between f1 & f2, you can call both methods one by one from original class.