Because the Patriots haven't had a very impressive roster in recent years, they haven't had many players that teams around the league were clamoring to trade for. They, of course, hoped to trade some of their better players anyway, wanting to add more draft capital to their stock, and that continued with Mike Vrabel this past offseason.
The new regime was willing to do what it took to make the roster what they wanted it to be, which included moving on from longtime fan favorites like David Andrews and Deatrich Wise Jr., and also meant trying to trade others they didn't feel fit their new roster.