

For the exact same reason that “fair use” is still so incredibly nebulous and twitch streaming/let’s plays still exist.
NOBODY is crazy enough to want to take that to the courts. Because maybe you get a judge who has “common sense”. Maybe you get an old white guy who thinks Pong was too complicated and decides that you are wrong. At which point you have now made a bunch of legal precedent for REALLY stupid stuff.
Its also kind of why so much stuff about video games actually never gets patented. It is playing with fire.
If you are thinking in terms of building a widget or making an industrial process, it makes perfect sense. Something like a wristwatch is the kind of innovation a LOT of people more or less simultaneously made and it is just impossible to definitively prove what country the first watch was made in. Even figuring out who was the first to file becomes a mess. Same with factory processes where the players who would even have the ability to iterate are often counted on fingers and toes.
But software (and research) in a global society is a real mother fucker. Because now the entire world can more or less see everything and reproducing things is fairly trivial. And… it isn’t like the patents actually matter all that much when so much gets done overseas. China Don’t Care but also the EU doesn’t really either and so forth. Sure there are avenues to try to pursue a studio using the patented Nemesis System but… at best you are going to be tied up in courts for years trying to get a judge to insist that a company in Germany needs to send you a check.