Maybe the Dev Team forgot about it, or they think it isn't important for a simulated A-10C or they just dont want to "spend more time"(=money) on something, which isn't lucrative to do.
But maybe.... ED really want's to make a simulation which gets improved until a fully functional digital modern combat aircraft simulation(Digital Combat Simulation?) is developed and implement it, like the missing TISL, IFF or the KY-58 systems.
Money makes the world go round and the military is paranoid by nature and maybe thinks that when we know how their "old" A10C works in detail,(like this missing ALT SCE feature) the strengths of this aircraft are diminished and so ED isn't "allowed" to implement this missing features.
added :
I also don't think that most people who use this software (most people = most money) are interested in this depth of fidelity.