The concern is that the US government will ask/force US companies to hand over data or give access even it's stored outside the US. E.g. see the "CLOUD act".

US law enforcement agencies have the right to come to your office, demand and collect all your data and force you to keep silent about it.

You guys in USA might not hear a lot about it but this is a business concern in a no small amount of countries around the world. Especially Europe (or I might think so because I'm there; selection and confirmation bias are always a possibility).