For what its worth, which is not a whole lot...
I think the Cowboys realize Jaylon has struggled. But it's hard to develop a player on the bench and he's a year behind considering his redshirt year, as far as contract ramifications are concerned. The Cowboys are trying to fast-track his development. The best way to do that is to put him out there.
On the outside looking in, that's a hard thing to witness when it cost you games, but at the end of the day, I honestly cannot say Jaylon's poor play has been at the heart of any loss. He hasn't helped as much as I would like to avoid it, but there are far more places I point the finger first before I point at him. I honestly think Heath has been a larger liability, but that is my own non-expert opinion.