There are cultural differences around smiling so its possible that they are trying to look serious and studious - assuming that the US attitude to smiling has changed over the years.<p><a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Smile#Cultural_differences" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Smile#Cultural_differences</a><p>NB On my first visits to the US 20+ years ago I was surprised at how you would get big beaming smiles* from people for no apparent reason... but then again I&#x27;m from a notoriously dour part of a dour country.<p>[*] I of course eventually realised that people were giving me big beaming smiles because they were paid to!.