Mock drafts at this time of the year are notoriously inaccurate. Mainly because most are based off of reputation and hype built before the season. People who do mock drafts are amateurs. Some more talented than others. But mainly it takes time to look at prospects as a whole and grade them relative to each other. That takes a lot of hours. And doing it in your spare time stretches that process out even more.
If you want to understand the mock authors to follow -- start by examining how they evaluate/review the prospects. And their understanding of what team's needs/philosophies are. The more detail into these aspects (not merely that a prospect is special, but in what ways), the more you're looking at an author that makes his own reads instead of regurgitating the latest groupthink.
As an example, Robinson and Peppers are undoubtedly two such groupthink prospects. Robinson could be sitting there are the #4 OT in a poor class. And the only one with significant red flags to boot. Robinson was a pre season all american and presumed to be the best tackle far and away in the class. Then the season played out. And the red flags settled. He'll drop like a rock.
Peppers is touted as an athlete. But this is a league filled with athletes. You can get elite for the NFL athletes in day 3 and develop those. Peppers has to fit somewhere and project to excel. You can't just be an athlete, you have to have other special qualities.
Now if you want to argue his ability to make plays and his general gravitas as an impact player -- that's a different discussion. At that point, you need a team able and willing to find a niche for him. Which teams in the early part of the draft are like that? Not many. Now he's falling not because of his ability, but of the teams willing to be unorthodox. Which is hard to justify to your fans when you've just spent a season sucking and have a lot of holes to fill.