Who says it was abrupt? They could have been planning this for weeks or months for all we know. In fact waiting till late on a Friday just before a holiday week to release the statement is more of a sign that this was deliberately timed.
A planned departure is practically never effective immediately.
If your goal is not spook investors and the public and raise doubts your company, the narrative is:
"X has decided it is time to step away from the Company, the Board is appointing Y to the position as their successor. X will remain CEO for N period to ensure a smooth transition. X remains committed to the company's mission and will stay on in an advisory role/board seat after the transition. We want to thank X for their contributions to the Company and wish them well in the future."
Even if the goal is to be rid of the person you still have them stay on in a mostly made-up advisory role for a year or so, and then they can quietly quit that.
The usual executive departure I have seen is all sugarcoated. Like XXX is having health problems so step down. Or XXX wants to spend more time with family. Or XXX now has a different interest and is leaving to pursue the new opportunity.
This statement doesn’t rhyme with planned transition at all.
