The sad truth is the 4-door, manual, FiST is exactly the wrong kind of car for the US market:
1a. Hatchbacks, especially small ones, are perceived as starter cars for starving students or deplorables by any other names. "Non-deplorables" drive mid-sized sedans or hybrid hatchbacks.
1b. A 2-door "coupe-like" but less-practical version would have enhanced perception of sportiness, so of course it was not offered
(2-door has superior side visibility and lighter weight too)
2a. Sporty cars are an ultra-niche in their own right, and while the FiST is the perfect combiniation of fun, affordable, sporty, practical, economical, it is simply not "sexy or powerful" enough to compete with any other car in the sporty segment.
2b. FWD cars are not perceived as sporty or performance-oriented in general
3. Gas is relatively cheap, most people looking for sporty cars are willing to trade off some mpg for perceived performance
4. Manual only car is an ultra-niche proposition in it's own right.
5. The suspension tuning is absolutely wrong for the mass market. It is not comfortable in the least under any circumstances (40-series tires only make it worse than it needed to be). Anyone still playing the "maybe a FiST" game up to this point will likely lose in the "Girlfriend/Wife Acceptance" round. (On the contrary, if there was one single thing that made me love the FiST it was the "perfect for my tastes" suspension tuning. VW Mk7 GTI was my frontrunner for a long time but it "needed" 3k+ suspension and wheels/tires upgrades to match the FiST driving feel. More features for less $, smaller, lighter, better mpg were icing on the cake)
5. Given all of the above, the price point must be extremely low. It's possible that Ford was making little to nothing on these "perfect" cars. And probably losing money on base Fiestas. Parts and labor are relatively cheap, so they probably couldn't make anything back through their service depts. Not to mention, a majority of FiST owners like to wrench their own cars at least some of the time (if not all the time)
As a reformed, lifelong VW fan, I would constantly lament the unavailability of the Polo GTi to the US market. Along the way, I learned and begrudgingly accepted why
The FiST is the strangest combination of "does everything exactly right for drivers while simultaneously doing everything exactly wrong for the market at-large".
/ramble off