If i'm not mistaken, because of this (via[0])
> The CLOUD Act primarily amends the Stored Communications Act (SCA) of 1986 to allow federal law enforcement to compel U.S.-based technology companies via warrant or subpoena to provide requested data stored on servers regardless of whether the data are stored in the U.S. or on foreign soil.
It sounds like compliance is only possible* if "the US company doesn't have any influence on the EU data-holding company" which is insane. This might be satisfied if the US company simply licenses their software product (e.g. the Uber backend) to an EU company. But this might not be adequate since chances are updates would be somewhat automated, and thus the US-based Uber might be compelled by the government to ship malware with their update to catch some US criminal (or otherwise enact some US spying).
* edit: only possible in lieu of a data agreement like Privacy Shield or its successor as mentioned above
0: top comment on https://news.ycombinator.com/item?id=33561222