Long before the clones started fighting the robots, Republic Troopers roamed the galaxy, keeping the peace with the aid of the finest weapons and sexiest armour this side of a Bounty Hunter. Let's take a look at how Troopers progress in Star Wars: The Old Republic.
You don't start out with the good stuff. You have to build to that. Troopers don't come straight out of character creation looking like the second biggest bad-asses in The Old Republic. They start off looking like the world's most inept Stormtrooper cosplayer. It's only when the character branches off into either a Commando or a Vanguard that they take on the appearance of soldiers somewhat reminiscent of guys we've seen in Star Wars.
Isn't this a military organisation? One would think there'd be a certain uniformity to the outfits. I guess the Republic just took a cue from Halo's UNSC and lets their people decorate their armour as they see fit. The enemy has a harder time returning fire when they're trying to figure out which costume is the coolest.