I can't agree with you, in the uk at least it was rare, but not unknown, to see such public displays of emotion prior to say the death of Princess Diana 20 odd years ago. At the time the events we saw unfolding were largely unseen in the uk, a term was even coined for it at the time - 'recreational grieving'. That sounds very crass I know.
I sure seem to recall a pretty elaborate ceremony for Mountbatten's funeral. Either way, you're not going to stiff upper lip yourself out of a mass murder, especially of children. Yes life goes on, but to expect the nation to move past with little or no ceremony is unrealistic.
I saw a scene on the tv news a couple of nights ago, a mother and young daughter placing flowers at some Manchester memorial site. Mum places her flowers down, young daughter then places her flowers down, steps backs and looks at Mum with an expression that says - Why am I doing this
I'd say you're filtering that through your beliefs. The child could equally have been non verbally conveyiing she needed to use the bathroom.