Halcyon, CoolerMaster has long made cases similar to it, but from steel, not aluminum. My brother and sis-in-law have a pair of old CoolerMaster cases from around '03 or '04 that look a LOT like the Mac Pro case design Apple adopted around the same time. The original CM-690 even shows some resemblance (aside from the looped handles/legs).
The real difference between such cases is the R&D time that was put into making the Mac Pro cases strong, quiet, and airflow-efficient. A similar case brought to the open market would probably demand a fairly hefty price premium, which would hinder its sales. It would likely be far more profitable to make something somewhat similar from less-expensive materials that can be sold at a lower price (and thus also likely in greater number) for at least equal or greater margin.
I'm a gamer and I do prefer cleaner designs. I don't mind the occasional LED fan or two, but for the most part, I prefer my cases smooth and sleek. I guess that's why I have a CM-690, an older Antec Sonata, and used to have a Tsunami Dream (no window).