Why does Andromache summon her son Astyanax from his hiding place in the collection, Thyestes; Phaedra; the Trojan Women; Oedipus with Octavia?

Andromache attempts to hide Astyanax from the Greeks in the tomb of Hector, but when Ulysses threatens to desecrate the tomb after Andromache tells him that Astyanax is already dead, she summons her son and hands him over to the Greeks.