Sports use different competition formats because the physical factors that decide the outcome are different in each sport.
Weight classes are used only where body weight strongly affects performance or creates safety risks.
Sports without weight classes are generally those where skill, speed, technique, coordination, and strategy matter more than raw mass or force.
The two condition that requires sports weight divisions, is Safety and Fairness. In Sports like Boxing, Wrestling,... more muscle mass = more strength. These sports requirs physical strike, throw, or grapple with an opponent, a heavier person can easily injure a lighter one.
In combat sports or strength-based sports, heavier athletes have a natural advantage. That's why they are seperated into different weight divisions.
Other sports is more based on technique and skills. Volleyball, Basketball, Soccer, .... Even very small people can be one of the bests. (Messi, Ronaldo...) In Tennis, a 60 kg player can beat a 80 kg player if they have better technique and speed.In Volleyball, height matters more than weight.