The Average Asian Aging Process

 Spoiler

The idea behind this is that since the skin on your tummy is loosened, your organs start to "lower" and "fill out" the space in the loosened skin which keeps it loose. So the cloth "tightens" the skin there so that there is support to prevent organs from filling out the space and so the skin can unstretch. ..... Or so my mother tells me.

It is true that tightening a woman's tummy primarily serves to prevent their internal organs from sagging down. It has no effect on the shrinking of the skin, however, if any, that would be providing the time it takes for the process to happen.