DBSS don't make sense in low interest environment..... DBSS makes some sense in high interest environment since HDB loan interest is 2.6%.
IMHO, DBSS gives the MOST PROFIT to developers because,
1) land bid lower, but yet priced almost close to ECs
2) easy to sell to average Singaporean, by saying can get HDB loan, thus very safe, i.e. won't get chased out if anything happens unlike private or EC.
Prime land should always be allocated for private uses or public amenities else government is encouraging people to use their 1st house as gambling bid to get future windfall..... just look at the silly Gen Y posting in Sunday Times 2 weeks back, give prime land to them and still bite their parents' hand.