Because the bulk of the supply is replacement supply, which means there will be replacement demand from those who scrapped their cars. The car population only increase marginally by 0.25%. On top of replacement demand, there will also be new additional demand by new buyers who are richer and more successful. Flipping of BTO flats also allows people to cash out and use the cash to pay for their new car's downpayment. New cars are luxury goods and is a status symbol.