He just doesn’t want to play Reyna and Pulisic at the same time, IMO. That or for some other reason he just doesn’t think Reyna would fit with his idea of how he wants the team to play.
Granted, that just a wild guess. But I think that’s why he hung onto Zardes for so long. Zardes wasn’t as good, but he best for the mold of what GB wanted at that position.
Regardless, I think it’s flawed thinking for a team with as little elite talent as the USMNT to not build the formation around whomever happens to be available.