Coe and Ovett were especially dominant at the same time from 1979 to 1981. Ovett had a three year win streak at 1500/mile going into the 1980 Olympics, so his superstar era began a couple of years earlier. Coe was not well known before 1979, so putting on match races in 1979 would not have made sense early on, and in 1980 they were not keen on giving the other guy an advantage before the Olympics. They should have raced each other in 1981. There was not Diamond League or Golden League in those days, but there was lots of money in appearance fees. There were also events like the World Cup and European Cup in which they would both be picked, but for different events. They both had an aura of invincibility that few athletes have. It would have been a major shock for them to lose a race. None of the guys running today have that, though Ingebrigtsen was almost there. Morceli and El Guerrouj had it. There was a race series of matchups set up for 1982 which unfortunately fell through due to Ovett's knee injury and Coe's illness issues. By the time they were both back to full health, they were still very good, but the aura of invincibility was gone.
While on the subject, people making definitive predictions for Paris based on a race in May might want to look at how Coe was progressing two months before the Los Angeles games.