Memory is not cleared when big batch job runs in sql server 2008R2

Hello,

We have migrated to sql server 2008R2 and I have set up my MAX Memory 32 GB and MIN left a default 0.

When I was watching performance while running big batch job, it was done within 30 minutes but memory was showing almost 30 GB in task manager and after it's ran, it was still showing 30 GB memory.

I couldn't understand why it's not releasing memory after job is done and still showing 30 GB memory into task manager?

Thanks,