We asked camera companies why their RAW formats are all different and confusing

One problem is that you cannot have a universal format that is both truly raw and doesn't embed camera specific information. Camera sensors from different companies (and different generations) don't have the same color (or if you prefer, spectral) responses with both their Bayer filter layer and the underlying physical sensor. If you have truly raw numbers, you need the specific spectral response information to interpret them; if you don't need spectral response information, you don't actually have truly raw numbers. People very much want raw numbers for various reasons, and also camera companies are not really enthused about disclosing the spectral response characteristics of their sensors (although people obviously reverse engineer them anyway).

What does RAW really mean then? Couldn't they simply redefine what RAW means to create a standard that can include proprietary technology? Like why not define it as including a spectral response?

There is no 'RAW' format as such. In practice, 'RAW' is a jargon term for "camera specific format with basically raw sensor readings and various additional information". Typically the various RAW formats don't embed the spectral information, just a camera model identifier, because why waste space on stuff the camera makers already know and will put in their (usually maker specific) processing software.

(Eg Nikon's format is 'NEF', Canon's is 'CR3', and so on, named after the file extensions.)

I don't know if DNG can contain (optional) spectral response information, but camera makers were traditionally not enthused about sharing such information, or for that matter other information they put in their various raw formats. Nikon famously 'encrypted' some NEF information at one point (which was promptly broken by third party tools).

> Camera sensors from different companies (and different generations) don't have the same color (or if you prefer, spectral) responses with both their Bayer filter layer and the underlying physical sensor

This is all accommodated for in the DNG spec. The camera manufacturers specify the necessary matrix transforms to get into the XYZ colorspace, along with a linearization table.

If they really think the spectral sensitivity is some valuable IP, they are delusional. It should take one Macbeth chart, a spreadsheet, and one afternoon to reverse engineer this stuff.

Given that third party libraries have figured this stuff out, seems they have failed while only making things more difficult for users.