According to Chip Kelly, the reason the Eagles used Matthews that way is because the team didn't want to give too many responsibilities to the rookie. "We just wanted him to play one position and learn one position," Kelly said at the NFL's owners meetings in March.
According to Matthews himself, an expanded role for the sophomore pass catcher could be coming. In a recent interview with Zach Berman of the Philadelphia Inquirer, Matthews revealed that he doesn't expect to be limited to the slot.
"I think you would think that I might get a whole lot more outside reps now just because [Jeremy] Maclin is gone, but I already had talked to coaches, and they were already going to implement me more on the outside as opposed to just the inside regardless. I don't think that's a crazy, huge deal."
It's interesting to see that the Eagles expected to move Matthews to the outside even before losing Maclin. If Maclin had re-signed, the team would likely have been returning their exact starting wide receiving corps from 2014 with Maclin and Riley Cooper on the outside with Matthews in the slot. Perhaps there would have been more of a rotation in place.
The same is possible moving forward, though the Eagles are thin at wide receiver without Maclin. Philadelphia's top three wide receivers now appear to be Cooper, Matthews, and Josh Huff with the recently-signed Miles Austin lingering in the mix. There's also the strong possibility of the Eagles add one or two more wide outs through the 2015 NFL Draft.
In any case, it'll be interesting to see how things work out. Matthews was very productive as a rookie in the slot; he finished with 67 receptions for 872 yards (13.0 yards per reception) and eight touchdowns. Matthews did a good job of working against slot cornerbacks, but will he be able to have the same kind of success on the outside if moved there? It's something he capably did at Vanderbilt, but it remains to be seen at the NFL level.