Malaysia Airlines owns the plane that created the data, therefore legally they own any data the plane creates.
You are right about NATIONS like Australia & the USA stepping up to help Malaysia.
But Inmarsat is a different case because they are involved in an indirect business relationship with Malaysia Airlines.
Inmarsat owns the satellite with NO data in it. They open their doors for a service business by saying if you pay us we will use our satellite to provide tracking data for you. One of their customers is SITA.
Malaysia Airlines owns a fleet that uses ACARS avionics. In order for the ACARS to function, they hire SITA to provide communications via VHF radio & satellite. SITA hires Inmarsat to provide the satellite aspect of the business.
A SITA spokeswoman released a statement that said,
"The Malaysia Airlines ACARS avionics communications via the SITA network is proprietary to the airline".
That means the Airlines owns the data that Inmarsat is "handling".
Since Inmarsat does NOT own the raw data that they are "handling", they WERE obligated to help through their business relationship & committments.