User blog comment:Lord Loss/Monster Hunter Theory... Blog/@comment-5043481-20121021210526/@comment-4212769-20121023142344

Easily explained:

Ambush predators are more agile monsters/animals that hunt equally fast or even faster, small monsters/animals so they need to surprise them to get them.

Akantor, Ukanlos and Deviljho are big enough to hunt monsters that are bigger and with that mostly slower monsters so they don't need to hide too much. Of course they are also able to wait for the perfect strike but especially Deviljho, I believe, isn't patient enough to make an ambush attack. And as all three can also easily steal prey of other predators so they don't need to hunt themselves but if necessary.