AWS often deploys its new platform products and latest hardware (think GPUs) into us-east-1, so everyone has to maintain a footprint in us-east-1 to use any of it.
So as a result, everyone keeps production in us-east-1. =)
Not to mention, even if you went through the hassle of a diverse multi-cloud deployment, there's still something in your stack that has a dependency on us-east-1, and it's probably some weird frontend javascript module that uses a floatilla of free tier lambda services to format dates.
So as a result, everyone keeps production in us-east-1. =)