Why is King Lear unable to recognize the Duke of Kent?

Readers have questioned why Lear is unable to recognize his familiar friend and loyal vassal the Duke of Kent when Kent returns to him disguised as Caius. Shakespeare makes it clear that Lear and Kent are very well acquainted in the following lines.
KENT: Royal Lear, Whom I have ever honour’d as my king, Loved as my father, as my master follow’d, As my great patron thought on in my prayers,--
Readers have also questioned why Lear is so gullible that he believes the outrageous flattery of his greedy daughters Goneril and Regan while failing to appreciate Cordelia's genuine love and honesty.
The Earl of Gloucester shows a similar gullibility in trusting his villainous son Edmund while turning against his loyal and loving son Edgar, then failing to recognize Edgar when the young lad appears as Mad Tom and assists and protects his father out of pure filial devotion.
Apparently Shakespeare intended for it to be understood that both Lear and Gloucester had been wise and shrewd men earlier in their lives but were becoming weak-minded in old age. This is the common denominator between the two characters. They are suffering from the early stages of senility.
Even in our own times, we see that old people are favored targets of con artists and are continuously preyed upon by petty crooks as well as sophisticated big-time swindlers. Not only that, but old people are frequently victimized by their own children, just as Lear and Gloucester are victimized in Shakespeare’s play.
Readers also ask questions about Shakespeare’s characters’ “tragic flaws,” as if Shakespeare was obliged to provide Lear, Hamlet, Othello, Macbeth, and others with their tragic flaws just because Aristotle decreed it almost two thousand years earlier. Shakespeare was a playwright, director, producer, actor, and even part-owner of the theater; Aristotle’s only exposure to the theater was sitting on a cold stone bench as a spectator. It should also be noted that Aristotle knew only Greek plays. Shakespeare deliberately violated Aristotle’s rules, as we can see in the way King Lear violates the sacrosanct Unity of Place by spreading the action all over the map of England.
Shakespeare seemed to favor mistakes rather than character flaws as the causes of his tragedies. Both Lear and Gloucester make glaring mistakes: Lear in trusting his two older daughters, and Gloucester in trusting his bastard son. Gloucester had also made a terrible mistake years before in engaging in an adulterous union which resulted in Edmund, who is directly or indirectly responsible for the deaths of Lear, Cordelia, Goneril, Regan, Cornwall, and Edmund's own father Gloucester. Othello made a mistake in trusting Iago. Brutus made a mistake in trusting Cassius and then another mistake in trusting Antony. Julius Caesar made a mistake in trusting Brutus. Cassius, mistakenly thinking the battle is lost, in effect commits suicide by having Pindarus stab him. Messala comments,
Mistrust of good success hath done this deed.
O hateful Error, Melancholy's child,
Why dost thou show to the apt thoughts of men
The things that are not? O Error, soon conceived,
Thou never com'st unto a happy birth,
But kill'st the mother that engendered thee.
Romeo and Juliet both died because of their mistakes. Macbeth was mistaken in listening to his wife and to the three witches. King Duncan was mistaken in trusting Macbeth and the vicious Lady Macbeth. Prospero, in The Tempest, was mistaken in trusting his brother Antonio and letting him run the government while he buried himself in his mystical books.
Lear fails to recognize Caius as Kent, and Gloucester fails to recognize Edgar as his son, for the same reasons that Lear disowned Cordelia and banished Kent, and for the same reasons that Gloucester was so easily turned against Edgar.