I've answered over 20,000 questions in the 'serious' sections of AB (i.e. outside of Chatterbank) but I reckon that this one must be impossible to answer!
That's because it calls for us Brits to understand American culture. We might admire Americans or despise them. We might love them or loathe them. But, I suspect, it's totally impossible for us 'reserved' Brits to actually understand them!
American culture has many influences, with many of the contributing cultures being far more 'demonstrative' than we're used to. For example, if you attend a funeral in the UK it's probably quite unusual to see anyone actually weeping. If anyone does sheds some tears they'll probably try to hide their emotions from others but, if you go to some Mediterranean or Middle Eastern countries you'll encounter people at funerals openly screaming, wailing and throwing themselves onto the coffin. America, through immigration from those countries, has a more demonstrative way of grieving.
Similarly Brits salute a sporting victory (e.g in county cricket) with polite applause, whereas people in other countries (e.g.Italy or Brazil) party on the streets all night long. Again, America seems to have absorbed such influences, with (from a British perspective) an 'OTT' way of celebrating victories, or even of simply greeting a musician coming on stage.
Like you, I see the American way of doing things as 'OTT' but perhaps that's because WE'RE out of step with most of the world in expressing our emotions.
Chris