No one is “forcing” anyone to do anything. It’s transactional. A car hire firm can’t force you to sign a document saying you will take responsibility for damage – they just refuse to rent you a car if you don’t.
It sounds like this block has been flagged as high risk due to previous claims so the insurance comany is saying if any committee members won’t sign, they won’t insure.
And if one committee member refuses to sign, the others are entitled to do whatever is required to get the insurance that the law requires them to hold.
Is the hold-out committee member trying to get insurance from another source? I would guess not.