I think you have the relationship between yield and demand backwards. The yield of a bond and its price are inversely related, so an inverted yield curve (lower yields at longer durations) implies the opposite of what you said: there is higher demand for longer-dated bonds relative to short-dated ones. One way to interpret this is that investors expect poorer asset returns in the short term, so they are willing to lock in a lower yield for a long period of time instead of, for example, taking significant losses in the stock market.