Why are Europe-US routes incomplete, but Asia-US isn't?


I’ve been using Flightware to look at flights and their airways routing. I’ve noticed almost all Europe-US flights don’t have the full route info. However, US-Europe does.

I know that Flightaware gets its data from the FAA so it’s possible only the portion in US airspace is shown. But I tried tracking some Asia-US flights and the full route is shown. So I’m not sure about that explanation.

What gives?

For example:

Europe-US, incomplete route: flightaware.com/live/flight/UAL902
US-Europe: complete route: flightaware.com/live/flight/UAL901
Asia-US, complete route: flightaware.com/live/flight/SIA2