'For marketing reasons' would be my answer. It makes the game stand out and gathers attention "0-2 players? Are you serious?" And this kind of thing.
It also tells you that, in the solo mode, you will be against an AI, and that the AI has initiative enough so you can even put the Beast AI and the Human AI one against another and it will still work. So it also advertises the AI. It's not something that merely reacts to the players' action, it's something fully operating on its own.
'Zero players'... 🤣 I see it says "with a hibernating beast against a robot miner" for zero players ... But why is my question? 😂