>>10062354This. With the fit of modern kits it takes only a few days to glue together an unpainted model, even if it's hundreds of parts. Then a reviewer can just show off the blank, assembled model, with the fit, and occasional gaps for everyone to see.
Also in-box reviews are kinda meaningless when the manufacturers, and sites like super-hobby just post photos of all the sprues, decal sheet and whatnot online.