The obvious difference is that SMB was a game, run solely for entertainment purposes and which has no impact on your daily life or productivity. We play games with the understanding that we're engaging in interaction with the software under a particular set of rules for the purpose of creating a challenging experience.
A computer is a tool and the OS is part of its utility. An OS that imposes artificial limitations on what the user can do is akin to a tool dictating how its wielder can use it. People using a computer are generally not interested in a constant game-like experience with arbitrary rules and limitations. If they want that, they can install a game on the computer and run it to get that fix.