Leases are risky things for the lessor...I have an in-house leasing company and it is always a fine line in being competitive in front, and losing your ass at lease-end. The Fseries has a long track record on residual value history,but with such volume the F-series has,if the residual is wrong just by a percent or 2,the losses could be huge at lease end.
Ford will run some lease programs on Fseries models from time to time,but with inventory low,why should they?
The Flex has no residual history,or sales volume to judge...but I predict the real residual values on the Flex in 36-48 months will justify my prediction.