A decade ago, when knee and elbow pads became popular with infantrymen, there were some problems. There were mixed reviews from users. Some troops, especially those who had been in combat, praised them, realizing that the pads prevented many minor, and some major, injuries.
Some younger troops considered the pads suitable only for wimps. There were also practical considerations that led to legitimate criticism. Extended use often caused the pads to slip. If troops tightened the straps too much, it cut off circulation. Overall, troops believed that knee pads were probably worth using but that the elbow pads often just got in the way.
In the last century, as infantry increasingly fought individually, running about looking for some cover, instead of marching in formation into battle, knee injuries became increasingly common. These injuries often led to no more than a limp. But on the battlefield, that could get you killed because it slowed you down. Troops also have a tendency to experience knee injuries that get much worse over time. These, decades later, can cripple the victim. An operation will install artificial knee components, but several decades ago, you just had a lot of former soldiers walking with canes or crutches. So in the short term, and the long term, the pads make life a lot easier.
Since then, a minor industry has arisen, providing many new, and much improved, pad designs. The latest ones use non-slip outer surfaces and, behind that, a new kind of foam that quickly changes shape as needed. The new pads fit better and last longer. Thus, after a decade of widespread use, you will find few infantrymen who disdain the pads, even the ones for elbows. The attitude now is that a savvy grunt does not go into harm's way without the pads.