Why the banks try to cover themselves for different transactions in different manner under the garb of different relationship?

Banks offer their services as debtor/creditor/licensor/bailee/trustee etc. These relationships are based on different enactments and mandates for different purposes and the intentions of the constituents. Thus, different transactions establish different relationships with its customers. This means that the relationship with the bank is based upon nature of transactions. Further, these also provide bankers with the protection under various enactments.