Why do no characters wear gas masks except citizens?

[ridiculous_ties]

It seems like a major over sight to me that even when the air exchange was a part of the plot that Alyx, Eli, Captain Vance, etc all do not wear gas masks, only the citizens do. Even the child models don’t wear them. Was there a lore reason for any of this? 

[Commander Booce]

It's called "plot armor" my friend 

Or, in this case: plot debuff for the citizens. (Serious answer: I have no idea xdd)

[PrisenShift]

Realistic answer: the game was in the beta