That or they are certain they will get burned sooner or later, and therefore even if they tank the value of their holdings it's at a time of their choosing and with an amount that's predictable.
Contrast with the scenario where they keep doing it, steadily increasing their bitcoin holdings and even seeing the proportion of sales using bitcoin increase… and THEN hit a wall, not of their own choosing, and see the value collapse.
Even if they are not dumping their holdings at all, there's still a case to be made for pulling a plug at a time they control, over an amount they control. If it collapses, they can put a hard limit on how much they lose: that being, the previous value of their entire bitcoin holdings.
