They did, well, sort of. They didn't really have a plan and their defense went from meh to completely terrible after the trade. Of course, no one plans to trade 2 young, former first round picks on the defensive line. Sweat was a solid player and Young still hadn't really gotten back to his old self before the ACL injury. It's possible the front office knew Rivera was basically on his last legs and would be gone at the end of the season and they were prepping for a new regime to come in and rebuild.