Jenkins was top 5 when looking at some mock drafts before or around the playoffs, I'm assuming that was because he could play. 40 times are why he isn't looked at like that.
Jenkins has been a bit overrated at CB for a couple of years. He's a great tackler, but doesn't have the cover skills you want in a CB in the NFL.
The bloom started to fade from his rose halfway through this CFB season. All the Combine did was confirm those thoughts, IMO.