Unstalling a wing is very simple, decrease the AOA to less than the stall AOA.
How right you are! But .......
1. Too late
You need enough aerodynamics on your elevator. You might not have it when in a deep stall, or when you are way too slow already.
2. Too little
You need the authority by the FBW. Its action computers might not have enough travel to cope.
3. Too 'magentised'
You need the authority of the protections. They might be fooled by sensors and not allow unloading, and/or they might be too complicated to override ......
4. Too inexperienced
You need the guy at the stick realise that he's in a stall! Even with 20k hours he might have been told this can't happen, or he might have never experienced such a situation, just read in the OM what to do in case the thing happens that can't happen per superior design ......
Pick your numbers, they pretty much apply for many of the latest accidents.