Because she's a severely emotionally damaged person who never grew up and is stuck in a warped and violent version of her childhood.
I suppose that depends on old Mary is (and the actor who plays her). If Mary was born in 1989, she would be too young to remember the 80s like that.
Silly isn't an inherently bad thing, threatening isn't an inherently good thing, and the two aren't inherently mutually exclusive. Silly can be threatening if it's in the right context with the right contrast, and threatening can get in the way of character sometimes.
And sometimes silly is just silly and threatening is kinda of a key factor with a villain.
Going back to TNG, the Ferengi were supposed to the main villains of TNG, they were supposed to represent everything that was wrong with unfettered capitalism, which could have been interesting, but they looked like little goblins and acted like monkeys in their first appearance and they were quickly demoted to comic relief.
I think the fact that guys like Stilt-Man, Matador I and Leap-Frog are seen as silly concepts is why they are no longer very relevant DD villains.
I think the Maleev costume is too bland.
It seems like a lot of on this thread disagree, what costumes are bland or have personality, is to a degree, a matter of personal taste.
I personally doubt they will go with the 80s look for the character though (when or if she shows up, she likely won't appear for a while, if at all). I a lot of 20 year olds may not get the reference to the 80s and I think the character looks stupid.
Also would Mary have big old 80s hair? Starlord may love the 80s, but he didn't have bad 80s hair.
