User blog comment:Kogath/Monster Hunter: World Discussion/@comment-6050823-20190728081447/@comment-25119729-20190730120957

You could make the argument that in the New World, Diablos have been uncontested for the Apex position for so long, they have become less aggressive and as such slower than Diablos in the Old Word. No need to waste energy to go fast when you have no enemies you need to use it against.