The reason the Eagles gave was "After careful consideration over this offseason, the Philadelphia Eagles have decided to part ways with DeSean Jackson"

I agree with you that they didn't want to pay $10million per year for Desean Jackson.

But $10million is about right for 1300 yards per season. It's not out of line. So either they don't think they need a 1300 yard receiver (doubtful), they think they can develop someone else to get 1300 yards(cheaper), which would indicate he's a product of their system or as the reported "rumors" they're worried about his gang affiliations (too risky).