If you watch, you'll see we all walk differently. The way we walk can be affected by aches, pain, stiffness, injury, surgery, habit, environment; leading to a limp, a weight shift, external rotation (duck feet), shortened step, the way our foot moves on the ground, our arm swing and so on ... This usually does not correct itself and can lead to further problems and impair recovery.
This could be gradual, built up over years of compensations, or as a direct result of injury.
Making improvements, and doing some simple movement practices helps regain a more efficient walking pattern, gaining freer movement, unlocking joints, improved elasticity, better proprioceptive feedback, balance and speed.