You're on social media.  
You've posted great new Steampunk photography.
Then somebody asks what Steampunk is? 
I don't understand it?  

There are many things I take for granted. Goggles being traditionally worn with Steampunk fashion is one of those "expected" norms, and required no further thought. But, if you're new to Steampunk.  Or, haven't  benefited from mingling at CON, the idea of wearing goggles isn't so obvious. 

C., wrote:

I’m not trying to tear down steampunk or anything, but what is it with (women) wearing old welding goggles as part of the steampunk look?  And many pair it with an old pith helmet?  Is it just because they are old items?  Or that they are related to outdated technology?  

Hello C:

I think your questions are excellent?  

Why Goggles ? Why pith helmets ?  And, their relationship to Steampunk?

In my opinion “gender” isn’t an influence selecting goggles or pith helmets.
I encounter an equal number of men and women that enjoy the style.   

There are as many “right” answers, as there are people who love steampunk. Essentially the central reasons are either actual/real historic associations. Or, an individual’s creative and imaginative adaptation of Steampunk tech and fashion into the genre. 

The Pith Helmet and goggles are generally accepted examples of retrofuturism. 

Speaking to the historic, and "loosely" so for brevity’s sake: Pith Helmets originated to protect colonial military (many nations) from desert and tropical environments; as a measure against heat stroke and sunburn. And, became equally popular with Victorian and Edwardian era civilians. The pith helmet developed from practical necessity. But, endures today representing the exotic and adventure so reminiscent of writer Jules Verne. 

As to goggles, think “practical” ! 
Goggles have both industrial and military applications, equally true during the 19th Century and now. Early aviators or people driving cars on dirt roads benefited from immediate eye protection. Adventurers, soldiers and those traveling into regions notorious for dust storms /habbos needed goggles. There many styles of goggles depending on personal tastes and budgets. 

From a Sci-Fi view; goggles are part of any “serious” Steampunk Airship uniform.  They are symbolic of  “Industrial” and “Empire” era societies, real and imagined. 

If you ask most people who wear goggles, Why ?  The answer is because goggles are fun and look awesome. Goggles adapt easily with pseudo-Victorian, pseudo Edwardian, Anime and Sci-Fi fashions.