I think technologically we've come to an impasse for the reasons you've pointed out, but I suspect that the average user also has little demand for drives great

I think technologically we've come to an impasse for the reasons you've pointed out, but I suspect that the average user also has little demand for drives greater than 1 TB in capacity which might be just as big a factor. I'm not saying that an individual's combined storage requirements don't exceed that but rather than no one storage need requires drives with a greater capacity.