What do you mean "suddenly"? I was running path tracers back in 1994. It's just that they took minutes to hours to generate a 480p image.
The argument is that we've gotten to the point where new rendering features rely on a lot more path tracing and light simulation that used to not be feasible in real time. Pair that with the fact that displays have gone from 1080p60 vsync to 4K at arbitrarily high framerates and... yeah, I don't think you realize how much additional processing power we're requesting.
But the good news is if you were happy with 1080p60 you can absolutely render modern games like that in a modern GPU without needing any upscaling.
Oh, now you're wrong. AI upscaling is demonstrably more accurate than plain old TAA, which is what we used to use in the previous generation. I am NOT offloading compelling NPC dialogue to a crappy chatbot. Every demo I've seen for that application has been absolutely terrible.