Because the popular raw development engines (including those built into the cameras that do the conversion to JPEG) aren't attempting colorimetric renditions. They're going for "pleasing" color, with everybody tuning their algorithms for their own special sauce.
What, you thought all those different picture styles were random flailings at trying for colorimetric accuracy?
They are different optimizations with different parameters. You would think that each company would offer at least one "colormetric accurate" profile, right? Actually, they are trying.
Since you cannot have color accuracy, going for pleasant colors is the right thing to do.
If your gray card isn't matching, you've got the worst gray card ever manufactured.
You did not understand what I said. The gray card might be perfect, you camera's filters are not. Not to mention your monitor or the inks of your printer.
But you also don't understand what the Luther Condition is, either. A camera that meets the Luther Condition will render metamerismic shifts the same way your eyes do. So the fact that the cameras display the same reaction to metamerism as your eyes just goes to further prove my point.Too bad such cameras do not exist, proving my point. Canon's red filter, for example, is much close to the human one than Nikon's. etc. 5D's blue filter is much cleaner than 7D's, one, etc.
Cameras are not meant to be spectroscopic instruments. They're designed to model human vision, and they do a damned fine job of it.
If you're not able to get quality colorimetric results from your gear, it's your problem. Your gear is quite well up to the task, I assure you. Granted, it's not something you can do with the software that comes in the box, and it's not something many people care about so the knowledge of how to do it isn't common. But it most definitely is possible with common off-the-shelf equipment.
Sure. Go to IR, download their RAWs and try to match the colors of different cameras. Good luck. And that is not even close to reality, where lighting changes.
Why don't you do the experiment I suggested: same scene with different lighting? If you are right, a simple tweak of the WB would match the colors perfectly.