None of Don's reasons
Jay is on the right track. Start with file size. Using 32 GB files, assuming the typically 100 MB full RAW file is ~120 MB, that is 266 pictures per 32 GB card. For every 10,000 pictures it would be 1.2 TB.
If needed, ok, buy bigger memory cards, more hard drives, and put up with the additional processing time. But a lot of time, for what I shoot, it really wouldn't be needed. I've seen a couple of comparisons of sRAW vs mRAW vs RAW and it is tough to see much of a difference. Nothing like jpegs.
The other reason is simply I would prefer a more flexible camera and the ability to make adjustments depending on what and how I am shooting. Getting that flexibility out of a single camera would be amazing.
If you stop thinking about 100 MB as resolution and think of the data simply as information, at full RAW, you would have 100+ MB of information for a given image. For a 100 MB camera, ideally it could then drop down to m/s RAW and have say 25 or 50 MB of information. If compressed well (and not throwing away bits), how different would that be from the current ~35 MB of information I am happily getting from my 5DIV?