Don't think it's that much a mystery why Slats didn't do that well in ODI's, myself. Aside from temperment, his game was geared to hitting the ball along the carpet and through the field for 4. Technically, in the early days, he was textbook but he just wasn't programmed if you will, to changing his batting position to turn a textbook forward defence into a nurdle around the corner, for example. He'd keep trying to hit the ball through the field in the early overs waiting for the right ball to smash, get bogged down, the field would crowd him then he'd get out trying to hit out.
Guys like Rick Ponting show it's not just about waiting for the right ball in your scoring area, you have to still find a way to score when the ball's not in your pet shot. Sweating on the loose one didn't really work for Slats because in ODI's, the bowlers aren't trying to get you out so J Random Bowler can sit back of a length for 10 overs, not take a wicket and they've done their job. Before you know it, it's the half-way point and you're scoring at 3 rpo and you have to hit out which is made more difficult by the field being back. Notice Matt Hayden had similar troubles until he developed some decent nurdles and cow corner shots.
Interestingly, he had a run of solid scores for Aus in ODI's towards the end as a lower-order nurdler/hard-runner. The field was back outside the 30 by the time he came in so he could avoid the 'crowding' effect and scored pretty well without being a bit boundary hitter.