Because if u no need to spent the amount for the postpaid plan, the phone price is cheaper.

Example digi postpaid 80 for 24 months can get samsung a15 for free.

First year got rebate 10x12 so,
70 + 6% tax * 12 = 890.4
80 + 6% tax * 12 = 1017.76
Total 1908

If just use prepaid plan say digi 25 monthly, 25x24 is 600, no 6%, then buy phone outright can get 790, making the total 1390, a savings of 518.

can change plan or port to other telco anytime coz no contract.