The point is that as CEO of a company you have a fiduciary duty to have the best interest of a company in your actions and behavior.
Having sex with your workers and chinese spies is obviously not the kind of behavior that reflects that.
And if companies did not fire their CEOs over such blatant missteps the wrong message would be sent to the whole corporate America.
It sucks because obviously Nvidia would be nowhere without Jensen, and it's not like he killed someone or committed fraud, but the mistakes have been huge none the less.
And don't forget that those are the two cases we know about, but when you see 2 ants in your kitchen there's always more.
And the internal investigation of Nvidia quickly assessed that the issue was bigger and Jensen was more of a liability than an asset.