Like eating, why some of them eat using chopsticks, others using fork and spoon, fork and knife, chopsticks and fork. Or shower/bathe, some are soaking in bathub, some shower etc. Or taking dump. Some sitting, some squating. Why is that? Why don't human invent one way to eat, taking dump, shower and use it throughout history. If you see different cultures has it's different way to live. Human sure is weird creature.