The laugh track has been a staple of modern sitcoms, including “Seinfeld,” for decades, but it often leaves a sour taste in the mouth of viewers due to its artificial nature. Some may wonder why “Seinfeld,” a show filmed in front of a studio audience and replete with gut-busting jokes, would need a laugh track at all. Luckily, Jason Alexander, who portrayed George Constanza, has an answer.