Part of it was that portraiture was considered a serious business. You wouldn’t sit for a painter with a s**t-eating grin, so you wouldn’t sit for a photo that way either.
Probably instamatics is what changed it. Once people were taking them on vacation everybody had to smile to show what a good time they were having, and it probably took off from there, all the way to Instagram.
3400 Russians were arrested as they protested the arrest of Putin’s adversary, Novotny.
https://wchstv.com/news/nation-world/protests-erupt-across-russia-demanding-navalnys-release