One of the main problems is that Jerry Jones has too big of an ego to give up much control.
The Cowboys have also been the same team for the last 3 years, which means they look good beating up on the average to bad teams, but they get killed facing any decent team.
The Cowboys need legit linebackers to stop the run, and Dak doesn't play well under pressure. Also, they are over the salary cap and won't be able to make any big moves because Dak is one of the highest-paid players in the NFL.
They also have to keep Dak for at least one more year because it costs them the same money to keep or release him, which is around $59 million.