Some (definitely not all) open source software lacks the other 90% of the stuff people want, including good design (visual or otherwise), good documentation, etc. Many new features that commercial software has are important (it's not obvious because different users depend on different sets of those new features).
The exceptions exist (for example, Firefox is well-designed, and has lots of new features), but they are just that - exceptions. Try to find a good 3D modeling package that's open source. Blender you say? Not many in the gaming industry uses, and that's because it simply isn't competitive with 3ds Max.
Also, some people (myself included) have moral problems with the GPL, so they try to avoid using GPLed software whenever possible. (Things are getting easier for me because most of the open source software I use today is BSD or MIT licensed.)
With a paid product, I know that I paid money and expect a level of support commensurate with that. I know that, if something goes wrong, I can pick up a phone and contact someone. The quality may not be great, but at least it exists.
With an open source product, that does not necessarily exist. I find myself searching through catacombs to find anyone that can respond to my requests. And immediate turnaround time? forget it. Even with the paid open source software, the turnaround time is terrible (take red hat as an example). Quite frankly, I dont think anyone who tried to sell open-source software really tried to solve the support problem.