There's some kind of a cognitive bias here similar to the base rate fallacy but not quite the same.

Yes, 40% is pretty high in the abstract. But a 60% chance of getting removed is insanely high compared to the base rate for this concrete case! Before this news broke, what were the odds of Huang not being a CEO of Nvidia a year from now for any reason. I'd definitely have taken the under at 1%, and the over maybe at 0.1%?

Like, what other risks were on the horizon? Him getting bored or tired? Not that man. A terminal illness that was diagnosed too late to treat? That happens very rarely for the ultra rich with their access to infinite high quality health care. A freak accident, e.g. airplane crash? Possible, but the rates are <<1%. Targeted violence? Unlikely, Nvidia is too far removed to be hated that strongly by anyone. The board firing him for some other reason? It'd have to be something that can't be papered over with hush money (e.g. any standard sex scandal almost certainly could; it's only the national security aspects that make it impossible here). A hostile takeover or similar that leads to him being ousted? Logistically and financially impossible.

Going from so rare it's not worth planning for to even odds is a pretty darn big shift from a single event!