Why doesn't StamDK have a stamina morph of Lava Whip?

I don't understand the reasoning behind some classes having spammable class abilities for any play style while others don't. And, the classes that don't have spammable class abilities do not perform as well as those that do.

Stam DK could use a spammable class ability that's MADE for it. NOT spamming venomous claw, which is a dot!