Other than it being futile to expect much rationality from Mr Market, I suspect that some portion of it can be put down to "risk on / risk off".

Good news? Knee jerk reaction to buy stuff that is optimistic and zoomy and growth oriented.
The latest news item makes it look like a recession is coming? The defensives hold up.

I think this view has some modest explanatory power, sometimes. For example, when Berkshire was a gigantic holder of Apple stock, it seemed oddly common for their prices to move substantially in opposite direction for weeks at a time. A higher Apple price should make Berkshire seem more valuable, but one is risk-on and the other is risk-off.

Right now the market is on a sugar high, which makes no sense to me on the surface of things. ("Good news! You have six months to live instead of three!") But it is what it is.

The VIX is back under 18 and the S&P 500 index is high and soaring. It's definitely not for everyone, but if one were ever to consider picking up a few "disaster puts", this might not be such a bad time to start considering it. This year's low may be below 4500 rather than today's 5900. Or not, of course.

Jim