They had a 13-point lead. A timeout might have helped the Cowboys have a low probability of improving the lead to 16 or even 20 -- which they did not need.
But a timeout (especially before the third down) also might have helped the Eagles reduce the lead to 10 or even 6 -- which they needed desperately.
Also, the Cowboys had the momentum. Why do something somewhat risky that might deflate them right before the half, when you don’t need it?
I think he believed in the momentum, and chose not to risk helping the Eagles.
His decision was to not risk reducing the 13-point lead. After making that decision, he managed the clock perfectly for it.
Argue that decision if you like, but don’t call it bad clock management. He managed the clock correctly to achieve his immediate goal.