They started using laugh tracks back in the 50s, but they became the standard in the 80s due to the attack on Fran Drescher. At that time, sitcoms were still commonly recorded in front of a live studio audience.
In 1985, she and her husband were brutally attacked in their home by two men who had stalked her from a live taping. In response, the studio went to a closed set for security and hired Central Casting “laughers,” that were eventually replaced by a laugh track. Other sitcoms followed suit when studios saw the ratings and cost benefits to a laugh track over taping in front of a live studio audience.