not regardless, but only if. The future is unknown, so their bet is also based on that unknown. Is it foolish? Who knows. Did nvidia seem foolish if somebody made that bet before their ai boom?
You can also just say things you don't understand are always created by fools.
Now, there are some fools buying these stocks. But to say that each one of these has a high P/E because every shareholder is a fool is very reductionary.
> these are real, well run companies with good fundamentals
I'm not disputing that. But even "real" companies don't warrant P/E multiples in the three-digit range, unless there's a very good reason to expect them to grow their profits by 10x or more in the foreseeable future – and that has to be the expected value of earnings growth (roughly, the average growth over all possible futures), discounted by the time value of the investment.
P/E multiples over 100 are practically never justifiable, except as "someone else will come along and pay even more" – i.e., the greater fool theory.
Essentially, investors buy as long as they think they will be able to sell at a higher price in the future, regardless of economic fundamentals.