Why penalise singles who buy new HDB flats?

I accompanied a relative to select a new two-room HDB flat and learnt that there was an additional payment of $15,000 for singles.

This is a penalty on a single person's marital status.

Singles who later marry a citizen will get this sum of money back in the form of a grant. But such unions may not happen.

Why is there a need for this singles premium?

Chua Lee Huang (Madam)