The problem for Microsoft is that branding only works if it's built off a solid, widespread product with a good repuation. Github Copilot might be solid but it's a niche product that most people have never heard of. So people wind up associating the entire Copilot brand with the mediocre to bad Copilot experiences they are exposed to on a daily basis, such as the useless Copilot button on Copilot+ PC keyboards.