Why don't we always get variable keys?

Hi,

I would like to know why the REST API (GET https://www.figma.com/file/:key/) response is inconsistent in terms of variables information it returns.

Let’s say we have a component which fill refers a variable created in the same file. In such a case we get variable id e.g. VariableID:1:10. However, when the variable is in the external file (exported library), we get the variable key e.g. VariableID:02d1b5ac60e4eca7753d5087fac6a14e9888eb4f/3:235 (02d1b5ac60e4eca7753d5087fac6a14e9888eb4f part). Can’t we always get variable key which is unique between Figma files?