I do think there's an element of random selection. I'm an elite on Delta and travelled the same route I've travelled many times (CMH-HNL) round trip, bought well in advance, purchased from the Delta web site, purchased wtih the same SkyMiles Amex card as always. I'd never been SSSS'ed on this trip before and BAM! There it was.

It took almost 30 minutes to be wanded and inspected. (Including the wanding of my bare skin because I was in shorts and a t-shirt. I wore no shoes but had to take a pair out of my carry-on bag to be inspected--even though I wasn't wearing any.)

I think it's just a way to inconvenience and humiliate as many travellers as possible so that nobody wants to fly and the industry can be further crippled. The TSA blames the airlines; the airlines blame the TSA.