Because *.dng is the Digital Negative file format created by Adobe.... This format addressed a hitherto unstandardised archival format for RAW camera data files, which used to be any one of a plethora of file extensions, *.cr5, *.raw, *.nef, *.raf, *.orf, *.srf, *.sr2, *.arw, *.k25, *.kdc, *.dcr, *.mos, *.pnx, *.crw, *.cr2, *.tif, *.mrw, *.pef, *.mef to name but a few, and is at least standardising the RAW image format across the board, and could potentially become the industry standard for RAW formats. Since DNG is an "open" file format what this means is that either Adobe's Camera Raw converter built into Photoshop, or any third party program that adopts this format, will be able to interpret and convert these files today, and in the future.

It's not a question of high end software as any Google Search will tell you that you can pick up inexpensive conversion software and also find other proprietary ways of opening any *.dng file.

Maybe I'm wrong but standardisation is surely the way forward when you are talking about approximately 70 different types of RAW file extension... Maybe....?