– Russians don’t smile unless there’s a reason. It’s a cultural thing. Look it up. They’re simply not big smilers. And esp. not with strangers.
– At the time, and throughout the 19th century, having your picture taken was similar in importance to having your portrait painted. In other words, it meant that you had to look formal and serious, because, well, it was a serious occasion
– Fast films really didn’t exist back then. Meaning you had to remain stiff and awkward looking in order not to blur the photo. Bulky, clumsy cameras didn’t help either. The easy to use and portable Kodak Brownie was only just being introduced to the market in 1900, and with perhaps a few possible exceptions, doubtless these photos weren’t taken by one of those.
All that said, i a few of the photos you can see a trace of a smile in a few of the subjects. Really, this was probably a novel and exciting experience for them.
Hope this helps.
Just a thought.