Why did Mencius think that Liang's method of governing the country could not increase the population of Wei?

Liang thinks that his efforts for the country should make his own people more than his neighbors, but obviously he has not achieved the expected results. Mencius told him the story of "taking pot calling the kettle black as an example", hoping that Liang would understand that what he did was obviously not enough, and that was what he should do as a monarch. What makes you think that neighboring countries will naturally decline because you have made some efforts? In fact, in Mencius' view, Liang's "moving millet" is not committed to governing the country together with the rulers of neighboring countries, and there is no difference in essence, but only in form and quantity. This implies that Wang Huiliang's small act of kindness will not increase the number of people. To increase the number of people, he must be benevolent and have the demeanor of a king.