"In 1999, the problem of poor fruit set was widespread throughout the Hindu Kush regions of Nepal, China, Pakistan, and India. Hand pollination was widely practiced through the entire region. However, by 2011, only apple growers in the Maoxian region of China were still hand pollinating."

Most varieties of pear are parthenocarpic.This would be fine for the peasant who didn't need to commercialize his pears The main reason for needing pollination would be to have fruit that is more regular in size,shape sweetness,maturation time,etc.The above quote states that hand pollination was already going on, which suggests that already there were not enough insect pollinators for mass production. Perhaps not a decline, but a continued low level of insect pollinators?