Upon investigating on this issue, we finally found out why we see this behavior.
In our project we have lot of Roles implemented (Business Roles, IT Roles, and SSO), so all our entitlements that are associated with Roles in IIQ will not populate in the remove access page.
If the entitlement is configured as requestable, IIQ will allow you to search and add through the “Manage User Access”, but it won’t give result while removing.
So the way to remove this entitlements would be if the roles are untagged from user’s cube automatically the entitlement would also get removed.