No really... Why don't cats wag their tails like dogs?

Why are they different?

My cat uses her tail to show one emotion. She whips it around when she’s pissed off at the dog, or me, or my son. She doesn’t like to be held or petted. So when that’s forced upon her, she gets really pissed off and hisses, whipping the tail madly.

She’s a bold and crabby little bitch that will walk right between the dogs legs underneath him and growl, sticking her face in his food bowl until he backs off with his ears down and tail between his legs. He’s a big dog! Nearly 100lbs wolf/shepherd hybrid mix. He’s really alpha around other dogs, and ferocious towards the mailman. But the little black cat has his number. Not uncommon to catch her chasing him across the room.

But the dogs tail displays all sorts of emotions… excitement, fear, aggression, happiness (it whirls in a circle like a propeller). Why don’t cats do this too?