Originally Posted by Alexrd
I thought it was to make it more recognizable to Star Wars fans (stormtroopers and clone troopers?).
As for the armour styles, there are lot of different styles that the Trooper has depending on what type of armour you pick up during the game... I'm playing as a Trooper Vanguard so I've already looked through some of what they have and their is a good variety. Some look familiar and have the style of a classic stormtrooper/snow trooper/scout trooper all the way to the ARC trooper variant clone troopers... and then there are trooper armour which look nothing like what the movies or other media have shown us.
As for the trailer itself, it's just as Alexrd said, they just went for a simple look that was recognisable to Star Wars fans in general which combined aspects of the storm and clone troopers as well as adding a little bit of flare not seen in either.