[throwawaysocks]

Most important reason: a lot of potential reviewers wouldn't like that model for a variety of reasons.

Reviewing, generally, isn't prestigious or well-rewarded. So potential reviewers need to be kept as happy as possible. Internet forums have a lot of frustrating problems that IRL conversations don't have, especially for people who wouldn't otherwise use an internet forum.

You have to remember that the people who enjoy participating in written conversations online -- even young people who grew up on the internet -- is still a small fragment of the population.