Because, you can buy LCD stands for multiple monitors and pick the monitors you want.
http://www.tigerdirect.ca/applicatio...947&CatId=2465 Or for a little more money, how about:
http://www.tigerdirect.ca/applicatio...276&CatId=2465 Plus, with the dual stands, most will support at least 22" monitors. The market for dual 22" monitors, on a single stand is essentially zero. 99% of people who have a need/want for dual monitors are perfectly okay or actually prefer to have both monitors on their own stand. It's just unnecessary packaging, and the only people who would go out of there way to buy a pre-assembled dual monitor set up are business men who have dual monitors at work and have no idea how easy it is to have dual monitors at home.