Sounds like Sam was attempting to fix the board membership.
OpenAI had grown massively since some of the board members were installed. Some of them were simply not the caliber of people that one would have running such a prestigious institution, especially not with the weight they had due to the board being depopulated. Sam realized this and maybe was attempting to address the issue.
Some of the members (ahem, Helen, Tasha and to a lesser extent Adam) liked their positions and struck first, probably convincing poor Ilya that this was about AI safety.
Being lightweights they did not do any pre-work or planning, they just plowed ahead. They didn't think through that Sam and Greg have added tremendous value to the company and that the company would favor them far over the board that added zero value. They didn't think through that tech in general would see rain makers and value creators being cut loose and side with them instead of figureheads. They didn't think that partners and customers, who dealt with Sam and Greg daily would be find the move disconcerting (at a minimum). They didn't even think through who would be the next CEO.
Maybe they didn't think it through since they didn't care. There was only upside for them since Sam was going to get rid of them sooner or later. They didn't see that having been on the OpenAI board was an honor and enormous career boost. Or maybe their ambition was so great that nothing mattered but controlling OpenAI.
Further, they thought that if they slandered Sam that he would be cowed and that they would retain their power. I wonder how many times they had pulled this stunt in the past and it worked?