Not sure why Cram didn't double up in 1983, especially when it was clear early in the season that both Ovett and Coe were having problems and might not even go. Yes, he was still young and hadn't doubled up before at a major championship but he had already competed in three major championships, including an Olympics, and won two Golds (Commonwealths and Europeans). Compare with Ovett who doubled up at Montreal at age 20.
Again Cram never doubled up in 84. In both 83 and 84 his build up hadn't been perfect and was missing some race fitness (more so in 84). Doubling up might have served him well as it did Coe in Los Angeles. Ovett was a 1500m runner in both 78 and 80 and only ran the 800m as a warm up (and yet won Gold in Moscow and silver behind a druggy in 78).
Cram had already ran under 1.44.5 in 1982, which was fast for those days (aside from Coe) and not much slower than Ovett's pb. I guess an early season defeat in the 800m to Koskei in 83, and more importantly, Gary Cook, at Crystal Palace made his mind up not to double, but he knew he was just short of fitness at that stage and he quickly improved. Two weeks after that Crystal Palace run, he beat Coe (clearly unwell, Peter Elliot, and Wuycke at Gateshead in one of the most memorable 800m races ever run in the UK.
A week after Helsinki, he smashed his pb by nearly a second and ran 1.43.61 - fater than Wulbeck's winning time in Helsinki - and beat Peter Elliot again (4th in Helsinki, probably a medalist if he had ran a more intelligent race).
So Cram would almost certainly have medaled in the 800m in Helsinki and have had a great chance of achieving the double, something neither Coe or Ovett managed - in fact nobody since Snell at a global championships. I guess at the time he thought he would have many more opportunities and was focused on winning a global 1500m title, but how much his legacy would have been greater today if he had doubled up and won two Golds?