At that time, FIVB also stipulated that volleyball players must wear long sleeves and long collars. That's not the case now.
Secondly, the physical strength of female athletes is not as good as that of male athletes, and their reaction speed is also slightly inferior. Physiological differences determine that female athletes are more likely to be injured in volleyball than male athletes. Especially in front of the net, compared with male athletes who are better at jumping in the air, female athletes' knees are more prone to collision and other injuries. Wearing knee pads can reduce the injuries caused by these accidents or protect athletes from injuries.
Thirdly, wearing knee pads is a kind of self-protection for athletes. Nowadays, many male athletes, both at home and abroad, also wear knee pads. For example, the Polish men's volleyball team and the Japanese men's volleyball team in the picture below. Another example is China's excellent attacker Shi Hairong.
Fifth, different applications of technology have also played a role. For example, men's volleyball team often uses diving to save the ball. When landing, the chest lands first, and the knees land less. Female athletes often use tumbling to save the ball for physical and physiological reasons. Knees are easier to land when turning over, and sometimes you need to kneel and jump forward, so wear knee pads. The picture below shows a famous player from China rolling forward to save the ball. You can see your knees on the ground as a support.
I said knee pads, and now I say stockings.
Silk stockings are more common among female athletes now because they love beauty. Stockings can tie up thicker legs, which is a visual bonus for female athletes with insufficient muscle lines. Male athletes' foot hair is much longer, so it doesn't matter what they wear, let alone the quality and color of their skin. Female athletes are relatively concerned. In the early days, some men's volleyball teams didn't wear stockings, so they were more relaxed when exercising. For example, Cao Ping of China men's volleyball team in the picture below.
Some female athletes don't wear stockings, such as the Cuban star Torres in the picture below.
But one thing can be mentioned, that is, stockings also have some anti-cramping effects, which are somewhat beneficial to female athletes who can't jump much or have insufficient muscle endurance.
Nowadays, in order to expand its influence, volleyball encourages players to dress naturally and highlights the appearance of volleyball players' temperament because they are more free. It's up to you to wear knee pads or stockings. So there is no inevitability and no hard and fast rules.