One of the pieces of wisdom behind people's inability to recognize Hazrat Mahdi (as) is that he is under Allah's protection

BUT ALLAH WILL HIDE HIM (HAZRAT MAHDI (AS) FROM PEOPLE AGAINST THE OPPRESSION, CRUELTY AND WASTE OF PEOPLE’S EARTHLY DESIRES. (Sheikh Muhammad ibn Ibrahim Numani, al-Ghaybah al-Numani, p. 162)