But this is not a characteristic of old movies alone. The idea of a man and a woman meeting, falling in love, and getting married all in the course of two hours has been going on in the theatre for hundreds of years. Take for example, Shakespeare's "As You Like It." Rosalind watches Orlando win a wrestling match and falls immediately in love. As she presents the gold chain she is wearing as a victory gift, Orlando falls in love with her. Of course there are many misadventures after this in which they all end up living in the forest with Rosalind dressed as a man (whom Orlando does not recognize). Rosalind's cousin, Celia, meets and falls for Orlando's brother, Oliver. Rosalind and Celia's servant, Touchstone, falls for the lusty shepherdess, Audrey. The play ends with a quadruple wedding -- the fourth couple being another shepherdess, Phoebe, who fell in love with Rosalind when she was passing as a man and who is tricked into marrying the shepherd, Silvius, who has been panting after and enduring the abuse of Phoebe for some time. Shakespeare's other comedies follow a similar formula. They are classified as comedies because they all end with one, but usually more weddings.
As another poster commented, movies and theatre are escapist fare. We go to see a play or movie, especially comedies and musicals, in order to be taken to another world where the heroes are handsome, the heroines beautiful, where the villain gets his comeuppance, and all ends happily. Don't question or overanalyze it. Just willing suspend your disbelief and enjoy it.
"All the world's a stage, and all the men and women merely players . . ."