I'll tell you why. Because although Trotter is a great run stuffer, he's a major liability in coverage and essentially has become a first and second down player. The Eagles are looking at other players with more speed in zone coverage who offer more versatility, are younger, and for cap reasons........cheaper. He's also had some durability issues in the past few years.
It's a business, plain and simple. He'll catch on somewhere else. He's 30 with maybe has a couple of productive years left.
Don't be suprised if Jevon Kearse is next to go as well. I personally feel he's been a major bust since coming to the Eagles and he has not lived up to his contract.