alt Hacker NewsCRAN is a weird universe, but not (just) for the reasons you mention. CRAN is still heavily human maintained which means that there's a high chance that an actual human will look at your packages (at least for your first package). This imposes a considerably higher barrier to entry than most package repos, and hence I suspect CRAN actually has a considerably lower percentage of slop.
Absolutely correct. CRAN takes down and rejects packages all the time for minor issues and violations of their rules and guidelines. And there are a lot of them: https://cran.r-project.org/doc/manuals/r-release/R-exts.html
The fact that there is a human (and one with expertise in R) reviewing each incoming package makes pure vibe coded slop much, much harder to get approved.