Currently archives often store audio uncompressed, in broadcast wave format. This results in much more e-waste, shelf space required etc. But they can't switch to just any lossless codec, they need one that can still be decoded 50+ years in the future.

The old specification document didn't specify everything, you needed to read the source code or compare with a working implementation. Will people still understand the programming languages current implementations are written in then? We don't know. So this document should be stand-alone, so one could implement a decoder from scratch (without any other reference) in the future.

With this document, archives can more confidently use FLAC to compress audio and thus work more efficiently.