I think the delay has more to do with which agent/player will blink first than anything else. No agent wants to be known as the guy who got less for his pick than a player picked AFTER his player so everyone plays the domino waiting game on the top picks.
The first pick signed a few days ago but that's the easiest first round signing a team can make because they agree to the contract terms before the player is even selected with the first pick. Teams do that now to avoid drafting players with the first pick they know beforehand they "may" have trouble signing on time. Unfortunately, the team with the first pick is the only one that has this advantage. After the first pick, it's all up in the air with each agent trying to get the most of their pick they can and most importantly not accepting a deal that is less than any picks after theam.
However, the major problem this year is most likely that several running backs were chosen in the first ten picks. I can't remember exactly but it seems like there were 3 to 4 running backs selected in those first ten picks. Top 10 Quarterbacks traditionally sign larger contracts than non-QB positions including running back. Most teams know that the difference between a star running back and a servicable running back is very minor (there are a FEW exceptions of course) while the difference between a star quarterback and a servicable quarterback can mean the difference between winning and losing.
The one good thing about this (I assume the CBA played into this) is that the teams have a "rookie pool" which helps set (or limit I should say) the contract options so teams have something to back them up on their side of negotiations.
Also keep in mind that most teams wait until right before training camp to sign their first round players and teams start training camp on different days which means some teams will not have to worry about signing their players until later than other teams. This is one reason why I doubt you will ever see the Cowboys start training camp before any other team. Stephen and Jerry would be foolish to do so.
I suspect we'll see a major domino effect of signings once more teams start training camp.