Why would you want to do that?

Having big concentrations of specialized hardware makes it much harder to attack using large botnets. The BitCoin network is not very large today but would already need around 250,000 CPUs to attack. Imagine if there needed to be 250,000 distinct miners to achieve that strength instead of relying on particular types of graphics cards. It'd take years to build up that many.

Having smaller numbers of larger scale, more professional miners has other advantages too - like they upgrade their software to keep up with changes in the network, new script types and so on. The recent sendmany changes show a good example of that - just a few people with a good understanding of mining had to upgrade for the new functionality to become available.