I agree with posters who pointed out Becker's wrong tactics of trying to outhit Sampras from the baseline, he was slower and had less power off his groundies (off the forehand side obviously, his backhand was better though), so it was a losing strategy.
Edberg kept Pete out of his comfort zone by rushing him and making him hit as many passing shots as possible (similar to what Navratilova did to Graf), so Pete never felt as comfortable as against Boris, who usually gave him enough time to properly react.
This is what Pete said about Edberg in his book which nicely summarizes his struggles against him.
"He was always trying to rush you. The most deadly thing you can do to a guy is take away his time—make him rush or feel like you’re swarming all over him. Stefan was very good at that. His volley was superb, especially on the backhand side, and he was a tough guy to lob."