Offensive and Defensive coaches never see eye to eye.
When you look at the makeup of NFL coaches, certain types gravitate to certain roles. The "Wine and Cheese Guys" end up coaching offense, and the "Tough Guys" coach the defense through intimidation. This will eventually, and most of the time without fail, lead to a rift in the locker room.
Colin Cowherd explained the Eagles situation right now, and what is going on between Doug Pederson and Jim Schwartz. Listen here for the full audio, and check out The Herd Podcast too.