Why do we still need CI or TPD if medical treatment costs are covered through Hospitalisation plans?

Kelly is correct.

A medical policy pays your doctor.

A CI policy pays your family for the loss of income incurred when one is ill.

You'll probably need to stop work for a period of time, and even if you return to the workforce, you may need to take a reduced salary or hours.

Life has to continue, the family still needs to pay for bills, liabilities, save for the future, children still need to go to school, you still need to retire.

So yes, it's extremely important to make sure your hospital bills are taken care of, but if you do fall ill, it is probably even more important your family doesn't have to then rely on charity from family members to continue living.

The lump sum (SA) payout for a CI / TPD can be considered as a replacement of loss of income as well as for non-hospitalization costs (eg if TPD means you survive but with significant decreased mobility then the SA can cover remodeling your house for mobility aids).