The reason there isn't a flat pattern solution is that there is not a on-to-one correspondance in distances between points on the neutral plane in the formed part and any possible flat pattern.
The reason for this is that the material thickness changes, not it's bent shape, and the thickness change is the result of a complex combination of deformations that is infrequently investigated using FEA tools because it's an elastic-to-plastic transition.
In typical forming operations, the flat pattern is just the same as the projected shape of the formed part, but with thicker material and some margin to hold onto or trim off.
PTC simulates this with sheet-metal form tools that simply replace the existing geometry with the as-formed geometry, but without consideration for the material thinning to the flat part to generate the formed version.
A similar situation applies to vacuum-formed items; there's no sensible flat pattern except a piece of material that is large enough to cover the mold and thick enough not to rupture when formed.