Why are the files only available for 48 hours?

The files sent from a master to his slaves have a 48 hours validity to avoid manufacturer update being released before writing.

Here is an article that explains the risks of writing an obsolete file :
​https://help.autotuner.com/en/articles/4027883-why-should-you-always-read-the-ecu-before-writing-the-tuned-file

Note that master files do not expire.