The Lotus 78 was setting the way for Formula One. It showed the potential of ground effects in 1977. The Lotus was, for all intents and purposes, the first real attempt at ground effects. Chapman and the Lotus developers realized they could gain some advantage of downforce without the heavier drag caused by more conventional wings. They were refining their ideas with the Lotus 79 for the 1978 season.
Gordon Murray - yes, the same Gordon Murray that designed the McLaren F1- was designing for Brabham at the time. He had a sense of what Lotus was developing, and knew the potential of ground effects. But circumstances required he come up with another solution.