In fact they are making them but they are way to overpriced for common buyer.
Custom made acrylic case are a little cheaper, but you need to make an effort to build it like i did:viewtopic.php?f=15&t=67099
Assuming that you need something more serious than internet/office machine, try Parvum cases. They seem to be well made:http://www.parvumsystems.com/
If you like to customize every inch of your case and pay less for it, make it your own case like i will.
Cases made by transparent plexiglass are good because they show hardware which most of people like to see and admire.
Bad side of transparent cases are cables and dust.
No one wants to see bunch of tangled cables and even beautiful piece of hardware covered with dust.