How is buying a copy of software which runs on my own computer different from buying a physical machine that runs on my electricity?
If this were using a company's servers, then fine. More power to them. In fact, that's a very fair way to do business. You're stepping in their own backyard and so they get to set the rules of the "house".
But when I run the software in my own machine, using my own processing power, while not using any online services that belong to them, how is it different than just buying a physical thing?
Your cone example is misleading because the melting is a natural consequence of the object existing at room temperature.
Software stays the same unless someone updates it. The copy of the software that I own (emphasis on "copy") does not naturally go through anything besides what the user does to it. If I disconnect from the internet, nobody can touch it.
Microsoft should have the full right to deny service to anyone, I don't think anyone here disputes that. But Minecraft is not a service, it is a good.