I mean ultimately we’re guessing at the rationale of the leadership of each of these countries - but I’d guess based on vaccination rates that Europe generally has less of an antivax problem than the US, so authorities there might be less concerned about vaccine hesitancy. Vaccine hesitancy in the US is also very regionally concentrated - maybe less so in Germany?

“COVID parties” are also a worst case scenario - I think the vast majority of people would just opt to not get vaccinated and live their lives as usual - which would lead to more outbreaks, deaths, mutations, etc.