Why is our retirement scheme interest so low at only 4 percent? Isn't it much lower compare to other countries?

Which countries are you comparing to?

There is always a balance, high risk high rewards or high charges.

E.g. India bank interest rates, Fixed Deposits have high returns e.g. 6%. But their rates are unstable, might change easily, some might even default.

On the flip side, look at their housing loan interest rates, 6-8%.