Second, because I doubt losing 250K transplants would affect housing prices as much you apparently do. A decrease in demand is one factor, but Utah's housing market is influenced by other factors, such as housing supply, economic conditions, and interest rates.
Given the current housing shortage and strong demand in Utah, a decrease in population might not significantly impact housing prices.
Instead, prices could remain relatively stable or even continue to rise if the supply of homes still doesn't meet the demand.