Most of the time, demands that a guy move up in weight are based on wanting to create a situation in which that fighter is more likely to lose. That's why you so often see calls for moving up come after a fighter has seemed unbeatable for a longish time at their own weight class.
People wanted GSP to move to MW to fight Silva, because they wanted him to lose.
People wanted Jones to move to HW, because they wanted him to lose.
People wanted Rousey to fight Cyborg at 145, because they want her to lose.
People want MM to fight at 135 or higher because they want him to lose.
That's not the only reason people would like to see guys move up in weight, but it's a big one.