I am not fully familiar with the whole story, but given the different paths Acton and Koum have taken (activism vs collecting cars and chilling on a boat) i wouldn't be surprised that they had a disagreement about whether to sell and one of them prefer to back down. who knows, maybe he even preferred to keep Koum's friendship. Their very different backgrounds also point towards different motivations in a situation like this. I don't know if I'm being silly cos I don't know how these things work, but I'm also surprised nobody has talked about this possibility