Why is the Fuji RAW file bigger than Sony and Olympus?

It appears that the Fuji raw files are not compressed.  Every raw file that I have shot is exactly the same size (26,246,816 bytes).  I even took a picture with my lens cap on and got exactly the same size (if any file could be successfully compressed, one that is total black should be the one).  By the way, all of my shots are in 3:2 aspect ratio.  The pixel count of my images is 4896x3264 or 15,9980,544 pixels.  I don't know how much overhead there is in the raw file, but I thought I would see what the maximum bit depth of the raw file could be.  If you assume a bit depth of 12, the minimum space you could store that data would be 23,970,248 so that could fit.  At a bit depth of 13, the minimum space would be 25,968,384 which could also fit.  At a bit depth of 14, the space required is 27,965,952 so that will not fit.

I have not seen anyplace that Fuji specifies the bit depth for raw files, so, based on the numbers above, I am guessing 12.

And as to the original question, I think it is that the raw files are not compressed whereas the other manufacturers are compressing the raw files.