Sure, there can absolutely be reliable sources of reviews. The problem is in verifying what is reliable and what isn’t. Why in the hell would I ever trust some random dude’s WordPress blog as a reliable source of reviews? I would have no way of knowing that companies aren’t paying you or giving you free products.
Outside of something like consumer reports, which has built up a reputation over a long period of time, how does one figure out that a source is reliable? Review the reviewers? Those reviews would just get gamed too.