Ford builds vehicles to generate Profit. New designs are funded by cash flow. With respect to products with high changeover costs (both to consumer and manufacturer) short product life cycles (like 2 years) is very counter productive for both profit and cash flow.
How long did Ford work on the Gen2 before releasing it to the market? ~2 years that we know about, right? Probably 2X behind the scenes?
The COGS of each one of our trucks is burdened with R&D and Corporate overhead to cover the enormous costs of launching a specialty vehicle like the Raptor. Ford has to sell thousands of these trucks before they recover those costs and while they may be out of the hole by now, I bet when I bought my '17 Raptor, Ford's balance sheet still had red brackets around the second generation Raptor.
Regardless of people's guesses as to what Ford's strategy is or isn't with the Ecoboost platform, they certainly haven't generated enough cash flow from the HO 3.5L platform in the Gen2 Raptor to replace it yet.
However, taking back market share in the compact truck segment - Ford Ranger anyone? - and releasing a compelling offering to the enormous and almost uncontested Jeep crowd - 2020 Ford Bronco - is a much more highly probable course for Ford, again assuming profit and cash flow a primary drivers for their decision makers.