Piercings, for some people, is just another way of self-expression, sort of going along with tattoos. Others, however, may do find that getting a part of them pierced will enhance their looks. For me, I have no piercings anywhere, other than my ears, which are ironically stretched, so I cannot speak for the people that do have many piercings on the face or other area's, that is just my understanding.
My friend has his eyebrow pierced, just because he believed it would look good on him, and it does indeed. In fact, I thought it made him more attractive, but some people just cannot get into that style, and I understand, the guy I'm with is the same way.
Every form of body modification goes back in time, not just gauges as you mentioned. Normal lobe piercings were mentioned in the Bible, for each time your lobes were pierced it was how many slaves you owned. Tattoo's are very old as well. Yes their are some piercings that are fairly new, like mirco dermals, but for the most part, all them are old.
Oh and since I'm on it, lobe stretching never really went "out" so they can't come back "in" but now instead of being used in tribes like they were, they are not being used for fashion (like other piercings) or sexual purposes. However, some tribes still use it today, just not nearly as common.