The first reason is genetic relationship. Many parts of our body will be inherited from our parents, such as single and double eyelids or the whole body will be similar to our parents, and even diseases. If your father's leg hair is strong, you probably inherited his father's leg hair, which is normal.
The second is the difference in androgen secretion. Although they are all men, everyone's figure is different and the secretion of androgen is different, which also makes the thickness of leg hair different. Generally, men with strong androgen secretion have thick leg hair, not only leg hair, but also a lot of hair will grow all over their bodies.
The third is that everyone's physique is different. In the world, although we look the same, everyone's physique is different. Everyone has a different reaction to the same thing. Therefore, the different thickness of leg hair is the result of different constitutions.
But no matter whether the leg hair is thick or thin, as long as it is healthy. Some men even like to have more leg hair, which makes them look more masculine and sexy. Of course, everyone has different views on this matter, as long as it doesn't affect life, these are irrelevant things. This is also the magic of the human body. Everyone's differences make each other look so different.