Never thought about that. Always wrote it all uppercase because that’s what camera maker Canon consistently does from what I’ve seen.
If I search for Canon raw on Google the Canon owned websites that I see writes it all uppercase; RAW.
One of their pages that I find even makes note of that:
> The letters RAW do not stand for anything – it's just a convention that RAW is usually written in capital letters – and the names of RAW files from Canon cameras do not end in .RAW.
I can only recommend to consult more trustworthy sources.
I'd expect a cause is that most camera makers are Japanese, and it's not uncommon in Japan to uppercase words written in Latin alphabet for aesthetic reasons