There have been many variants that emerged in the US[0][1], but none of them have been significantly more infectious than the original Wuhan variant (until the Epsilon variants emerged very recently). Most of the ones that are more infectious than the Wuhan variant got nuked by even more infectious variants from elsewhere. I think perhaps the impression that there haven't been any variants stems from the fact that none of the big variants of concern have been from the US, which appears to have just been luck.

[0] https://en.wikipedia.org/wiki/Variants_of_SARS-CoV-2

[1] https://www.nytimes.com/2021/05/14/health/coronavirus-varian...