Movement and exercise put incredible force through the knee joint. Walking puts 4x the force of your bodyweight on your knee. Running 10x, jumping 20x. You need all of your muscles working effectively and all of your joints aligned correctly to help distribute this force.
Knee pain occurs when the strength, co-ordination or alignment of the knee joint is compromised and force cannot be dispersed evenly.
While joints such as the pelvis or shoulder are extremely complex, knee joints are relatively simple. They pivot in one direction & they are designed to work hard. Even long term knee issues resolve quickly with the right treatment and rehab.