After Losing Two, they still had 4 TE's on the Roster.

But apparently with Sims being more of a WR, they felt they needed another. I am sure they want to limit Higbee too & this has given Hopkins an opportunity to shine and so far he has, but McDonald is more of a traditional TE then Williams and has more experience playing TE at a higher level then Kalinic so the addition makes some sense.