Why do people still buy bonds, i.e. Singapore Savings Bond?

One potential advantage is that the bonds are 'fixed interest' so the 2.x% is payable throughout the 10 year (in your example) commitment.

For the rates on savings accounts/FD - they are non guaranteed so if the economic environment changes, the rates could be lower in future and total interest less than the bonds.

For endowments, assuming issued by an insurance company, they are guaranteed as well so comparable and any difference of yield should be attributable to credit/liquidity risk.