It really wasn't. It wasn't normal to install arbitrary applications on the computers in your fridge, dishwasher, game consoles, flip phones, washing machines, etc. Platforms have varied over time in how open they are to having other people developing for them. iOS is an example of a more closed platform and has shown that closed platforms can be successful. You can see Windows as a more open platform in comparison which was also successful. How open a platform is comes with different trade offs.