The easy answer, even though it sounds "stupid" is that Watkins body-type is so off the bell curve when it comes to the position that it literally scared the hell out of pro-personal.
For years business automation buyers were well aware of the phrase, "No one ever got fired for buying IBM"...
Well it's the same here. It's easier to "sell" a 6' tall 200lb FS to the rest in your organization that it would be to "sell" someone shaped as differently as Pat Watkins.
So most personel departments--- fearing the fallout from drafting an athletic oddball like Pat Watkins-- just avoided the problem by not drafting him.
But I can tell you right now there are other teams out there seeing what this kid is doing in training camp and kicking themselves for not dropping a 4th or a 3rd or even a 2nd on the guy.
This kid has the chance to be a difference maker for any defense-- you just watch.