Because good QBs don't fall off a cliff when there are 1 or 2 injuries around them. Sure, there tends to be some drop-off (not always), especially if it is a very significant player, but they don't go from very good to very bad. If they do fall off like that, it indicates that their success was much more dependent on others than is typical.
There's no denying that the Eagles still had a pretty good team. But there's no denying Dallas did as well, and that would be especially true if Dak was who people want to think he is. A good team played well, and a capable backup had a good run. Compared to a supposed good QB fell off a cliff.
You’re welcome to your opinion of course. His play does need to be better when things around him fall apart.
What I don’t agree with is the idea that Dak is only a product of his environment. What I mean is, not every QB could play as well as Dak did, when things were going right around him. Not every QB is capable of playing the way he did in 2016 and the first half of 2017. Even with the same help that Dak did around him.
So, what I find unfair about some of these evaluations is how quick people are to blame Dak for his poor play the second half of 2017, when he didn’t have his supporting cast. But
then don’t want to give Dak any credit for how he played when things were going better. And say it’s all because of Zeke and the o line. As if any scrub QB off the street could have played at the same level even with that help. Again, football is a team sport. NFL offenses don’t produce at the level the cowboys did in 2016 and the first half of 2017. Without the QB doing some things well.
I also don’t agree where you said good QB’s don’t fall of a cliff. You’re right, good QB’s don’t. But young QB’s go through stretches of bad play and challenges all the time. It’s part of being a youn QB in the NFL. It happens all the time.