It's not that long IMO, it's been 2 years since Nvidia stock took off, and at that point OpenAI was valued between $29B and $86B (compared to $500B today), so I'd say we've entered bubbly territory around then.
Personally Im not surprised. Im bearish on the capabilities of LLMs given the amount invested, but, I also believe theres about 2 years left (of minimal progress relative to money invested) to go before things finally start to crater.
Uber was in the red for like 10 years, and burned 31B, and complaints of it popping were constant. But here we are with it still going and now profitable.