Guess you need a primer on the differences tween raw files and rendered files. Raw files that have not been demosiaced are indeed small bcause the raw data hasn't been turned into RGB pixels yet. Once a raw file is rendered into RGB pixels, you get a much larger file, 8-bit is actually more like 3x the raw file (although that changes based on compression options when saving and whether you have backwards compatibility turned on or off). A 16-bit file will be 2x the size of an 8-bit file–again, depending on compression options. Saving a raw file in a Smart Object makes the file sizes swell considerably because it has to save the a copy of the raw file inside the rendered file plus any layers plush a composite preview.
So, what you've discovered is, it's useful to keep a raw file raw until you need a rendered file. When rendered, you'll have to expect the file sizes to be much larger...