Jared Lloyd makes a list of plausible reasons why we don't get a lot of folks to stick in NFL--through the draft or UFA routes.
http://www.heraldextra.com/sports/blogs/jared-lloyd/byu/lloyd-five-reasons-why-byu-football-players-aren-t-being/article_5a5a9e87-7160-5f34-91c8-0ccf319556e6.html?In a nutshell (and expanding on his reasoning), he compares BYU's placement success of draft and total current roster players with Utah, Boise State and Utah State and posits 5 reasons for the lack of production:
1. BYU lifestyle, resulting in selection bias--assuming top athletes don't want the BYU lifestyle.
2. Age. Older potential draftees both have a shorter shelf life and have less uncertainty about their productivity potential. Those extra years demonstrate what a player is really capable of, and the draft is a gamble: a GM would rather take a lark on a kid with slightly lower demonstrated ability but greater uncertainty around his top-end potential.
3. No national splash. BYU hasn't done anything really noteworthy.
4. Lack of Speedy players.
5. Injuries.
Our discussion of attracting "talent" is addressed by 1 and 4.
Personally, I concede that BYU's experience is different from U/USU/BSU in points 1 and 2, and different from U/BSU in 3. But Lloyd doesn't make the point that those comparators' experience has been different for 4 or 5, and I don't see it, particularly for 5. Have other teams not had injuries? In fact, it was an injury that opened the door for Ziggy to rise up and eventually be drafted.
I don't like being below Utah or Boise State a bit. But it's another level of aggravating that we're getting shown up by Utah State. And I haven't seen any good explanations of why--except maybe 1 and 2.
One last thought. Bronco has always developed the team as a team, not as individuals. He's not developing for the NFL, where individual talent matters (Lloyd touches on this briefly). That could also be where NFL-calibre talents like Cameron Jensen choose not to stay around--the premium placed on individual talent doesn't sit with the "team first" indoctrination of BYU's program.