It also may depend on peering arrangements Hetzner has. If EU ISP more inclined to peer with Hetzner than US one bandwidth in EU will be cheaper for them.
- in EU there are large peering exchanges to swap traffic
- in USA no peering exchanges exists and you need to pay for your traffic most of the time. Few big operators in US and they enforce this.
Looks like some deal wasn't renewed and they lost a big chunk of cheap pipe or/and some of their upstream providers decided to do something with routing.
Also, Hetzner is way bigger in the EU than in the US. Good access to services hosted by Hetzner is thus more relevant to EU ISPs, because customers in the EU will probably use more services hosted on Hetzner infra. This gives Hetzner more leverage in the EU to negotiate beneficial conditions with regard to its uplinks and peering agreements.
