Because every contributor has to be contacted and agree to the change. If one can't or won't your only option is to revert their changes and everything derived

Because every contributor has to be contacted and agree to the change. If one can't or won't your only option is to revert their changes and everything derived from them. This is yet another way the OSI was a bad idea. For a while they approved a bunch of open but incompatible licenses that couldn't be changed