Because the customer in question raises questions of the CEO's judgement, plus the possibility of knowledge that the target was violating sanctions. We don't know. That's why it's a bad situation for the stock.
The stock seems to be responding more heavily to the potential loss of Jensen than it does to the potential continuation of Jensen given new knowledge.
It also seems like there’s a high potential for half of Jensen’s position to be granted in a subsequent divorce decree, meaning there could be enormous selling pressure in the next several years.