I believe this is because the current state of things on the web advocates for consumption instead of curation, and you can see this trend in every domain not just movies/media. Multi-billion dollar corporations do not want their investments subject to a random person's criticism, and from their perspective that makes perfect sense. It was very prudent and certainly much cheaper to coopt the entire field of media critique: Metacritic is owned by CBSViacom, Rotten Tomatoes is owned by Comcast, IMDB by Amazon. The old-media reviewers can get drowned out by new-media that is beholden to these corporations for access to interviews, swag, early-access, exclusives, etc. The corporations that create the media own the algorithms that tell you if the media is good or not.

The vast majority of the web has devolved similarly. Interested in a widget? If you Google "Widget Reviews" the first page is drowned out by listicles. Google gets the ad money, the listicle website gets the referral money, Amazon gets the retailer's cut plus maybe another Prime membership. There's very little incentive for fair and honest criticism on the web and every incentive for the big players to drown it out.