Q:

Why does raw to jpg conversion differ in different editors?

I just started using RAW files (to be more correct I set my camera to RAW+JPG). Then I opened the raw file in RawTherapee and without doing any changes I exported it in jpg next to the jpg file generated by the camera. I expected these two files to look the same, but they did not. 
The one was a little overexposed and other had changes that I cannot describe. I thought that RawTherapee does not work well. 
So then I tried Darkroom. I opened the raw file with Darkroom and exported in jpeg. This file also had a little different exposure compensation compared with the original jpg, and with the jpeg from the RawTherapee. 
Then I also tried Photoshop and again got a little different image. 
I expected all these editors to produce the same jpeg but they do not. Why is that ?
I noticed that for the same raw file, they auto set different values for some of the parameters like exposure compensation, contrast, blacks, and other. Maybe there is some setting that I need to set to tell the editors to produce the jpeg exactly as the camera did or maybe I am missing something ?
EDIT: Inside the metadata of the raw file there is a tag MakerNotes. This tag contains nikon data that is described here: http://www.exiv2.org/tags-nikon.html It has a lot of camera settings that are stored inside the medatada in the raw file. So I tought that the raw editors can read this data and preset the sliders to this values as a starting point.
EDIT:
I found this link that answers my question: https://photographylife.com/how-to-get-accurate-nikon-colors-in-lightroom
EDIT:
I just found out that if you import canon or pentax raw file in lightroom it looks very close (not to say exact) to the image that you see on your rear lcd on your camera (the image that you expect to see) but this is not the case with nikon because nikon algorithms are proprietary and canon and Pentax gave the algorithms to adobe. So it seems that the issue is purely technical and just for nikon. There is a debate about this here: http://www.dpreview.com/forums/thread/3197480?page=5

A:

You can get different JPEGs from the camera, depending on the camera settings.
In many ways, raw converters are like film developers. It would not be reasonable to expect exactly the same results even from 2 different mini-labs printing the same negative, using the same paper and the same chemistry. But the sole reason for the existence of different film developers is to produce different images.
Every cameramaker changes their in-camera JPEG engine once in a while, sometimes between camera generations, sometimes with a firmware upgrade.
If you are not into reproduction, there is no right or wrong; there is "I like this more", "I like this less", "I do not like it at all",... There are also bugs, like premature clipping of the highlights, wrong black levels, incorrect midtone calibrations, poor colour transforms, ignoring sample variation. Decisions "in bad taste" happen too, (even) with the raw converters recommended by the cameramakers (that includes in-camera converters). Fortunately, off-line converters are rather flexible, and it is not hard to get what you want out of them.
If you happen to like JPEGs out of camera, you can use the recommended raw converter, as MBaz so rightfully points out; or you can try Adobe emulation based on reverse engineering of in-camera results, those are available under "Camera Calibration", in "Camera Profile" drop-down. Choose there something other than "Adobe Standard" and see how you like it.

