There is your reason, sometimes you just have to roll with history and gut. Of the 3, I'd say Slaton has the best chance of falling off. Not the most durable in the world, could have over performed a bit last season.
Chris Johnson has a ton of hype, but is still in a RBBC, which added yet another runner...and in looking at his numbers a few red flags: 1) while his overall numbers were great, he did suffer from some inconsistency last season. 2) he had a couple great games in the 2nd half, but he also failed to break 70 yards rushing in 5 of the last 7 games he played in. He also may find it hard to match his 10 TD's from a year ago.
In all of that, I don't find reason to downgrade these guys.
Slaton has durability problems? He overperformed last season?
How can you say that. We have no idea what his ceiling is. He has only played 1 year at the NFL level, and he was spectacular. That might not even be the best he has to offer.
As far as Chris Johnson being inconsistant, I think if you look closely at anyone's numbers who was outside the top 5 you can find some negatives. Those end totals are what are really important. Yes, it would be nice if a player who scores 160 points over the course of the year would score exactly 10 points a week. You're just not going to get that though.
Hell, look at DeAngelo Williams. He was the
top scoring RB last year. He had a 7 game stretch, where 5 of the games he failed to cross the 70 yard mark or hit the endzone.
As far as CJ's 7 game stretch, it was a tough road. Outside of the 2 HUGE games in there, he did struggle. He only found the endzone a few times and struggled to break that 70 yard mark. Keep in mind that 3 of those games were played against teams that were very strong against the run. His worst game of that stretch was against Chicago(5th), followed by NYJ (7th), and Jax (14th). If you're an owner with options and you're playing CJ against Chicago and NYJ, you have management problems, not player problems.