[weavejester]

People have mentioned perceived value; i.e. a fork of bitcoin would only be worth something if people generally agreed it was. However, there's also another reason, and that is that the security of bitcoin is directly related to how many people are using it. In order to double-spend, you need 50% of the CPU of the system, so the more CPU power you have on the network, the more secure you are from double-spending.