Because the future doesn't arrive everywhere at the same time. If you were in Ancient Greece you could have made the exact same argument about what is the UK o

Because the future doesn't arrive everywhere at the same time. If you were in Ancient Greece you could have made the exact same argument about what is the UK or Western Europe today. And so on. Clearly the spread of humanity from some point of origin is the reason and there is no hard rule that things can only get better, as you are currently able to observe in person.