I have watched these more then once....someone, anyone please tell me what has changed? Why is this kid who threw rockets on target, now seemingly cant hit a bull in the a** with a bass fiddle right in front of him? I swear, this all goes way deeper then Dak is a bum and can't throw with accuracy. I see the same Dak, then as now and there is something terribly wrong with this system.
Here's my answer to your question:
1.) Protection. A quarterback is more likely to complete passes without pressure than he is with pressure. Dak benefited from better pass protection his rookie season than his 2nd and 3rd year.
2.) Scheme. It takes a team a good year to get tape on a player. Teams evaluate those teams in the off season to determine a quarterback's tendencies and then structures game plans to attack a quarterback's weakness. Teams didn't have enough time to evaluate tape on Dak because - obviously - they can't really focus on one player or one team when they have to prepare for other teams week by week. But in the off season, coaches have more time to look at schedules, look at their opponents and devise strategies to exploit their weaknesses. So let's take Dak for example. Teams now had 16 games on film on Dak. They can analyze his foot work. They can see what routes he likes. They can see every component of his throwing motion, how he moves in the pocket, etc. Now, they have a better grasp on what he likes and doesn't like, what he can or can't do. They KNOW Dak doesn't like to throw interceptions. So, if a receiver isn't clearly open, he's likely not going to throw it. So they design packages to put pressure on him early and then cover his short, relatively slow receivers to not give him an option. He will hesitate and either get sacked or run.
3.) Confidence. A quarterback simply can't play the game of football scared to make an interception. This is admirable, but it also can be a liability. Dak is PETRIFIED to make a mistake. He doesn't trust his arm or trust that he can exploit a window. And because he doesn't, and because he may not be getting time to throw, he holds the ball. Yes, a quarterback should be considered about interceptions. But a quarterback cannot OBSESS about making interceptions. I think Dak is more troubled by this than other quarterbacks.
4.) Care-free. This relates to No. 3. I think Dak was looser his rookie season. He really had nothing to lose. If he failed, Romo would be back to save the day. If he succeeded, he'd be given the keys to the Cowboys kingdom. But as they say, it's harder to repeat as a Super Bowl winner than it is to win the first one, so too, Dak is finding that it's harder in Year 2 than it was in Year 1.
5.) Romo. I honestly believe that Romo's coaching helped Dak in his first year. I think Romo was always in his ear. And because Romo was, when it was time to come back, Romo didn't pull a Brett Favre or a Joe Montana - both of whom were very hostile towards Aaron Rodgers and Steve Young, respectively. They were less than help to their understudies. Romo wasn't like that, which is why he didn't really, openly fight for his position when he healed from his injury.
6.) Injuries. The offensive line isn't what it was Dak's rookie season. We don't have a receiving threat like Dez Byrant was in 2014. Our receivers are average. And if you're an average quarterback, you're subject to the talent around you.
Those are my takes.