No one was expecting a business earning $20B profits per year to go to zero.

What changed were the expectations of what their profit will be in 5, 10, 20 years.

> What changed were the expectations of what their profit will be in 5, 10, 20 years.

The funny thing is, that's a bad bet. Large tech company profits can last for years and decades. The archetypal example is IBM. They've had some years or record losses, but overall, look at their yearly profits:

https://companiesmarketcap.com/ibm/earnings/

We're talking about probably more than $250bn of profits over 20 years.

Just having a profit is not enough to say something was or was not a bad bet. I doubt anyone is happy with their bet on IBM in the past couple decades. A riskless bet on SP500 would have delivered far greater returns.

It also depends on dividends. If IBM consistently gave dividends to its shareholders, that could add up to a lot of money.

IBM is a good dividend stock. That said, there are certainly stocks you could have bought and held over the past couple of decades (as well as many index funds) that would have had better returns overall.

But it did not add up to a lot of money, compared to alternative, much less risky investments. In fact, it added up to a loss.

https://dqydj.com/stock-return-calculator/

IBM has objectively been a terrible investment for many, many years.

So... As valuation for those companies usually go, if the profit stays constant on real terms, the reasonable price to pay for the stock is often some 90% down from the peak.