Why could the "magic" never return?

The magic could never return because it was only an illusion. When the engineer decides to visit the family he'd been waving at all those years.... they were not what he expected. The mother and daughter were put off by his visit and fixed him with hostile looks. When the engineer finally leaves, he is visibly shaken from his experience, as the one aspect of his life he believed was pure and beautiful was merely an illusion. For the engineer, this revelation makes him realize that he has lost all hope, and that he will never be able to see the good in life again.