You made me curious about this, and so I did a bit of research. It seems to be a problem of sampling bias. Either you're not looking at enough photographs, or folks -- as they are today -- were reluctant about having their photographs taken when they weren't looking their best. Even today, people with acne tend to be more reluctant to have their pictures taken.

We know acne existed -- and was a persistent problem -- at least as far back as ancient Egypt. The Ebers Papyrus references it, as do Aristotle and Hippocrates. Pliny and Celsus used the term "varus" for acne. Shakespeare references acne in Henry V: "his face is all bubukles, and whelks, and knobs, and flames o' fire."

If you're interested in the early history of acne, I suggest this paper from the Proceedings of the Royal Society of Medicine. (It's a PDF.) I found it pretty informative, and you might as well.

Aside from what was already mentioned, keep in mind that prior to the invention of the digital camera, people were much less likely to be photographed, especially when unprepared, and most photographs from that era that you can now find were of adults in their 30ties and beyond (politicians, movie stars, military men etc.)