"How did AI video generation get so good in only a year?!?!"
Oh, that's easy. The impressive Sora videos you've watched are just existing videos, with tiny alterations applied.
I fact, the weird AI nonsense you see are the changes. The AI just made the videos worse.
Somewhere out there are videos of a lady walking in Japan at night, dogs playing in the snow, and a cat waking up it's owner. Sora took them, added weird looking stuff, and OpenAI posted the results.