I think I have the answer...
I used to recruit ETLs on-campus after I finished the internship program and I noticed the same trend in the candidates I was passing through the first leg of interviews. I noticed that candidates who looked more presentable had a higher level of communication. They were confident, ambitious, and less likely to choke-up during interviews.
The ETL position is nearly 100% social - gaining buy-in, engaging and inspiring, driving for results, collaborating, etc.
I'll pick on Engineering majors because they usually had the most difficulty:
Your typical Engineering major is focused on analytics. They aren't prepared on any social level through their upper-division coursework, and it was almost impossible for me to make eye contact with them while recruiting at career fairs. Communication is a skill that takes much longer than others to fully develop, so as a result Target focuses on hiring candidates that already have this skill with the intention of building up less significant skillsets during training.
It's not that ETL's are all attractive - if you threw them in a t-shirt and jean khaki's without any accessories, hair products, loafers or makeup they'd look like regular TMs. The blonde business major got the job because she was prepared through half her coursework being focused on corporate communication and organizational structure.
ETL's carry themselves professionally knowing that the expectation is for them to LOOK like managers. I think consumed TL hit the nail on the head with this one.