
Frank T. answered 08/19/19
Ph.D. in Film & TV Studies (UCLA) with 35 years of Teaching/Publishing
Fortunately, I happen to be an expert on both cinema AND boxing, since my dad was a boxing manager during my childhood.
Since the late 1890s, boxers have worn GLOVES, which cushion a blow to a certain extent -- for both the puncher and recipient of the punch (the "punchee"). That may be why the bout you saw contained no knockouts. Also, professional fighters develop defensive skills that often mitigate the effect of "power shots," which may end up landing on one's arms, shoulders, gloves, or as glancing blows that do less damage.
Depending on the movie, the knockout punch may be exaggerated, esp. if it only takes one -- which may be a "sucker punch" that takes the victim unaware. Most recent movies have added a slightly realistic touch: after the hero punches the villain, he (or she) grabs his hand in pain. A bare-knuckle blow hurts one's hands!: