There's a melody from the Carmen Overture in the Matador Song? Why?

Because Carmen's opera has a story that centers around bullfighting. [edit] Act I There is a bridge in a beautiful square in Seville. To the left of the guard house there is a tobacco factory. Mikayla comes looking for Don José, but instead of finding him, she is harassed by naughty soldiers and has to leave and come back later. José has come to relieve Moraré, whose superior officer is Sergeant Zuniga. The female tobacco factory workers pour out of the factory during their break, when Carmen appears, and all the men come here to woo her, except José. But Carmen has her eye on him. (Habanera: "Love is a little bird.") Mikayla, who is in love with José, brings messages and greetings from his mother (Don José: "Tell me how my mother is.") After she leaves, there is a brawl at the tobacco factory, and Zuniga captures Carmen, who at the time was trying to threaten his own workmates with a pocketknife. She was guarded by José, but José could not resist the temptation to let her go. (Seguidilla: "By the Walls of Seville...") [edit] Act II Evening at the smuggler's hotel, with the song and dance of the gypsy girls (Carmen, Fasciada, Mercedes: "The rattling, ringing tambourine."). The bullfighter Escamino arrives and is greeted by a hot line. They sing the matador's song ("To the fight, torero"). Dancairo, Raimundado, Carmen, Fasciada, and Mercedes decide to form a smugglers' ring. But Carmen refuses to join because she is waiting for José. José goes to jail for her, and after his release from prison José arrives in the area, but the call to arms is also sounded at this time, and Carmen stops him from reporting for duty. (Canzonetta: "Halt, who goes there.") Zuniga appears out of nowhere, and in a fit of rage Jose draws his sword against him. But the sergeant is soon disarmed by the smugglers, and José has no choice but to join up with Carmen. (Duet and dance, Carmen, Don José: "I will dance in your honor.")[edit] Act III In a valley, José moves in with the smugglers (sextet and chorus: "Listen, comrades "), but Carmen no longer loves him. She is now in love with Escamino. (Trio, on playing cards: "Shuffle, shuffle, cut them, cut them.") Smugglers stop the duel between José and Escamillo (Duet: "I am Escamillo." ) Mikayla arrives (aria: "Here is the smugglers' stronghold") and tells José that his mom will die soon. José viciously threatens Carmen and leaves the brigade. [edit] Act IV The plaza in front of the bullring in Seville is crowded with matadors marching outside the arena. Carmen agrees to Escamino's marriage proposal on the condition that he returns victorious. As she is about to enter the ring, she bumps into a pale Jose. (Duet, Carmen, Don José: "Is it thou; it is I.") José woos Carmen one last time, but Carmen refuses. So José plunges a dagger into Carmen's chest, and when the victorious Escamino returns to the square, Carmen is broken. Finally, José surrenders himself to the soldiers and the tragedy of this love triangle comes to an end. Reference: Guide to the Opera, by Leo Meriz, 1921 edition