Bending the knees is not always bending the knees.
Keep in mind, ‘bend your knees’ means having the ankles and hips in the correct position as well. If the knees were bent but the hips are not pushed back/down and the ankles are not properly flexed, then bending your knees might not be a good thing.
The knee is a weight transferring joint, not weight bearing. The femur connects the hip joint to the knee joint; the hip joint is the weight bearing joint.
The concepts above will change dramatically your way of moving. These concepts are nothing new in martial arts, but are mostly forgotten by instructors and practitioners.
Of course it takes time to change your structure and the use of the body. Old habits are difficult to remove from your brain.
Start slowly without too much power and have patience.
Why bodyweight more on the back leg
When body weight is on the back leg (70% more or less), we can store energy in the leg by dropping body weight into hip-knee-ankle. Each segment of this body part has a function. We cando not change the functions otherwise we will abuse our body.
Rebound the stored power
Dropping body-weight is a matter of moving a rectangle formed by the points of the shoulders and the groins. The knees are staying in the same place.
Taking the initiative
Sometimes we have to take the initiative when the opponent is passive.
Opponent can resist without pushing forward or just trying to use an “empty” posture.
In these cases we can use another way to rebound by using a drilling action in the legs. The picture makes an idea but is not completely accurate how the spiral is going down and rebounds.