why everyone assumes every fighter fighting below the weight limit will be drained?

Both of those catch weights were not necessary and were purely moves to gain a slight edge over their opponents.

 

And Pac was bloated. If I'm not mistaken, Pac had to go up 2 divisions from lightweight and Oscar down by 1 division from light middleweight. Are you saying Pac should have gone up three divisions instead of fighting at catchweight?

 

Every fighter is different. Some fighters cut a lot of weight so it's harder to lose that extra pound or two, others lose it easily.

Catchweights have just become annoying in general because of the frequency of them and the number of divisions out there. Catchweights have always been done but it seems like the past few years there's been so many.