Some customers want a white upright piano (please just accept this fact). Whether deciding between a Yamaha U1 or Kawai K3, however it doesn't seem to matter what brand, few dealers in Singapore carries white pianos.

White finishes are one of the most difficult, as they will show every tiny little finish flaw. Its more work for the manufacturer, thus, higher price for the dealer. Every manufacturer does finishes in "runs" (except for the most expensive hand built piano). IOW, 70 black pianos, than 50 mahogany, etc. If there is no other white piano being made, the cost of doing just one is very high because it interrupts the factory flow. It may take almost as much time as finishing many pianos in another finish.

One reason for not carrying/selling white pianos is low demand. Typically, white pianos don't sell very quickly, and they'll sit on the floor for ages just hoping for a home. Different areas of the country sell more white pianos than others. Its a personal preference.
The dealers pay more for a white piano than they do for an ebony polish or wood grain finish piano. Why is this? Ebony polish piano finishes are the easiest for manufacturers to do. Wood grain finishes step it up a bit - the manufacturer has to be careful that the veneers look good, match, etc.

Another reason for not carrying/selling white pianos is resale value. Apparently white does not go with as many room decors as black pianos and therefore is not as popular and does not sell as well. Resale value would definitely be less. Your decoration choices would be limited as well, though we've seen more white pianos in Floridian-style homes than any other. And the white color is easy to change yellow color after time beings. So we will be very hard to resell the white pianos.