Why has the Covid curve flattened in Europe but not in USA?

But the curve has not flattened in Europe!

At least if you consider France to be part of Europe: https://www.worldometers.info/coronavirus/country/france/

Or Italy: https://www.worldometers.info/coronavirus/country/italy/

Or Spain: https://www.worldometers.info/coronavirus/country/spain/

Really, what are you talking about? What countries do you include when you say Europe?

I am honestly confused, because I also looked up the UK, Russia, etc. None have flattened their curves.

The US got a late start dealing with the virus because of a failure of leadership at the very top. The president downplayed the virus and failed to lead an effective response to the virus early on. That delay in widespread testing, preventative measures like promoting masks, social distancing, minimizing gatherings, and the like should have started in January or February. Instead he left it to individual states, and the lack of a unified effort likely thwarted our progress fighting the virus.

Even 7 months into the pandemic we still don't have widespread testing or contact tracing, and there is still no coherent national strategy, and instead it is left to states which have different approaches.

In talking with my wife about it (she was not born in the US), she said that Americans really emphasize individual freedom more than in other countries, which is evident in people protesting against masks. In other countries, there is a sense of "we're in this together" and there is more cooperation with national or international efforts that help the greater good. In her home country of the Philippines, quarantine measures involved restricting travel between towns (similar to what was implemented in Italy). I am certain that would result in widespread riots in the US.

I have read that people who wear masks are still getting small amounts of virus particles when they are out in public, and as a result they are developing at least a weak response. This results in less severe illness when/if the person receives enough of the virus for it to become infectious.

I don't remember where I read this, or I'd post a link. Either way, it is an interesting theory which has not (yet) been proven.