why are sti's only in 4 door

I have a civic hatchback so I dont really understand anything that has to do with rally cars or anything of that nature. why do STI's and EVO VIII's only come in 4 door? i like sti's but i would never get a 4 door, is it like weight distribution or something?

From the rally perspective, cars do have to be a certain minimum length for the World Rally Car class, 4 meters. Smaller is better, but Subaru no longer makes a hatchback or coupe, and Mitsibishi is sticking with the 4-door Lancer for now at least (As the street Lancer gets bigger and bigger, they are rumored to be contemplating a move to their Colt/Cyborg hatchback).

It's mostly marketing: Subaru didn't feel the need for a 2-door or hatch anymore, and Mitsubishi likes the Lancer. If you'll notice, the French teams (And Ford), who mostly sell cars to Europe where smaller cars are more common, are the ones using 2-doors. Obviously the Mitsubishis and Subarus work well enough, no matter how many doors they have.

WRC regulations call out that the car must be a 4-seater in standard configuration.
Subaru developed the Impreza coupe of 1997 through 2000 in league with Prodrive & STI to give them a stiffer basis to build the rally car off of, the 4 door of those generations had more body flex in it.
The 2001 onwards Imprezas were designed with the WRC applications in mind, so when they designed the bodies they were made a lot stiffer, this is a benefit that carries over to the road counterpart too.
The current 4 door Impreza is 80% stiffer in the body than the coupe, and stiffer means better handling on the race course(and road).

To compete in rally the car needs four seats and why not make the car practical and have four doors. Plus having four doors is cheaper when it comes to insurance.