Its about being waterproof. You climb into the suit and you only have two openings. one for your face covered with a hat or secondary hood. the second one is in the chest covered by a rain jacket or poncho. most of the time you are hunched over forward protecting both the head and chest hole. Under heavier rain you can actively protect both openings as they are both within reach.

Its also a suit that a single person can get in and out of without any secondary help.

Its a good system that looks weird as fuck.