I can see Hinckley,Jr overhearing too many exasperated “if only someone would ...” as his brother and Bushes discussed dissatisfaction with Reagan.
And Hinckley decides to be the “hero” who’ll clear the way for better things.
History is filled with plots against leaders by trusted lieutenants.
Being shot could have stressed Reagan’s health even worsening his early Alzheimer’s.
If Bush was behind it don’t U think Hinkley would have used something more powerful than a .22?