Only if by "uniquely American" you mean also British: https://www.verdict.co.uk/robocalls-malicious/
And Canadian: https://globalnews.ca/news/6136318/canada-telecom-robocalls-...
And German: https://hiya.com/blog/2017/12/01/one-ring-scam-makes-way-to-...
And any other high-value target.
No matter the scam, scammers go where the money and the people are.
US population is ~5x greater than the UK, while UK GDP per capita is less than the US. More generally, the per capita economic posture of the US is strong compared to the top 10 most populous countries in the world. If you were an opportunist robocalling scammer operating on a purely probabilistic model, the UK would be a pragmatically irrelevant target. The situation in the US isn't helped by regulatory capture either.