A. Because they won. Not great at self-reflection, these mythical heroes.

B. It was, sort of, later on, and dependent upon your perspective. Especially by the Romans, when they claimed Trojan descent.

• Virgil, Aeneid Book 2 line 44: The Trojan horse is described by Laocoon as dolus, or a fraud, deceit, wicked wrong.
• Virgil, Aeneid Book 2 line 18: The inclusion of Greeks in the horse's belly is described by Aeneid as furtim, or like a thief (fur).
• Virgil, Aeneid Book 3 line 273: Odysseus/Ulysses~~/the cheat~~ is described as saevus, or savage, a term usually associated with non-Romans or animals. His land is cursed by the Trojan refugees as they sail on by. Took them significantly less time to get there than it took him.

There is, of course, the famous Roman saying 'Never trust a Danaan, even when bearing gifts' which comes from Laocoon's speech, shortly before the sea serpent eats him.