seats, interior, MFT, different looks, more power to show off, already has some of the mods in place and makes it easier to transition into stanced (Suspension, lowered already, a few stiffer braces and reinforcements that you won't have to deal with), and wider array of mods already supported even though it's a 2014.
I actually had a 2011 SES and upgraded to this car literally because of all these reasons. The ST was everything I wanted my SES to be and then some. Also, paying $240 a month VS trying to save 1000+ USD for each big mod I was planing on doing was a good argument for the ST as well. Granted I'm still doing mods so nothing has changed there, but it's already done some of the work for me which is nice.
I'm not saying you don't have a valid point, and I too am curious seeing as he is basically driving a sportscar like grandma on a sunday, but there are plenty of reasons to go with the ST. Mostly the supporting mods. the 2011-2013 Fiestas have maybe a quarter of the mod support that the ST has. And I know this because I was desperately trying to get my Fiesta turbo'd and kitted out similar to an ST. There are not a lot of options unless you want to take away all luxuries and then pay out the ass.
Oh and I actually looked at that purple Fiesta and the LAPP one as inspiration of mods that I was working on with my last Fiesta.
the LAPP one was at the same show:
EDIT: I dun got Ninja'd by the post above me.