.....but all rack cases are steel, most consumer electronics cases are steel, most computer boxes are steel.......well some of the above are available in plastic (blimey, don't tell me we are talking Teflon cases:o).
The reason I prefer steel (apart from the fact I have a tin ear) is that it is way way way easier and cheaper to finish than aluminium. And it's cheaper to buy too. To get anything to stick to ally AND look great you need either need specialist paint, luck and/or a dab hand. Check out powdercoated ally and compare it the powdercoated steel and I'll bet you that the steel looks a 1000% better. Your only real quality finishing option is anodizing, plating or polishing........
But true, aluminium (to my limited knowledge) is not magnetic.