I thought extra resistance was helpful for ski jumpers. The extra surface area of the loose suits allows them to jump further soooo maybe loose helmet straps help.
I live next to a small jumping hill so I can ask someone. My guess is no one knows or cares.
My cycling heel says on the run in in a tiny amount of drag slows them down and turbulence in flight is not good.

Theynuse extra surface but it's smooth. I don't see straps helping in the same way.

They're looking for maximum Lift/Drag.
A bigger smooth suit that doesn't flap excessively may well provide additional lift without a proportionate drag increase. Something like a helmet strap will only add drag. There's no up side to that.