The point is that they convey information without building trust. Research has shown that face-to-face contact is essential for building trust, because there is a lot of subconscious emotional information conveyed in body language. E-mail and other electronic communication conveys the factual, logical information, but not the emotional information. So if you want representatives to collectively decide things based on what is rational and logical but not be subconsciously influenced by lobbyists or other politickers, cut the emotional channel out of their communications.

It's the same reason that Google makes promotion decisions by a committee located on another continent. You want people to judge based on facts and not impressions, so divorce the objective facts from the subjective impressions.

Some of the decisions can not be actually made based on facts, such as decisions about future performance of some person (there are no facts that can guarantee it) or future effect of certain policy (the facts may be lacking or subjective and depend on interpretation). So, unfortunately, in many aspects in the politics "decisions based on facts only" are just not possible.