Why in combat sports the heavier the weight cl the more gaps until there are no limits?

As the weight gets higher, the less advantage it is to be heavier. Here's an example, say a person is 100 lbs and they fight a 150 lbs person. The 150 lbs person is 50% heavier and probably twice as strong. Now if a 250 lbs guy fights a 300 lbs guy, the 300 lbs guy is only 17% heavier and probably only 10-15% stronger. Also, there gets a point where being heavier tends to cause worse cardio, so it can actually be a disadvantage. Lastly, there just isn't enough big guys in the fight game to make a bunch of weight cles. I suppose it's because big guys don't tend to get bullied as much as kids, so fewer take up martial arts to protect themselves.