It is because of a simple mathematic calculation.
If a shipper is shipping a parcel worth of MYR1,000, and the shipping fee is MYR20, the profit margin for the carrier is probably just MYR5 or lower. If the parcel is loss or damage, and the carrier were to pay the shipper the value of MYR1,000.00, the carrier will need to make 200 deliveries just to breakeven. Imagine if the lost/damage parcel is worth RM3,000 (e.g. Laptop), the carrier will need to do 600 deliveries to cover back. That is a huge lost for any carrier.
Carrier are certainly responsible to the unfortunate event, hence they provide default liability coverage as listed below.
However, similar to Travel Insurance, which is normally available during purchase of flight tickets online, travellers are encouraged to insured themselves with travel insurance provided online. The coverage includes flight cancellation, delay, natural disasters, etc. Similarly, shippers are encouraged to get their own parcel insurance coverage like travellers getting the travel insurance.