> arXiv doesn't need much. All they do is host static pdfs uploaded by someone else with free CDN services from Fastly [0]. I'm sure they could get academics to volunteer moderation services as well.

This just isn't true. arXiv nowadays has to deal with major moderation demands due to the influx of absolute drivel, spam, and slop that non-academics and less-than-quality academics have been uploading to the site.

Moderation for arXiv isn't perfect or comprehensive but they put so much work into trying to keep the worst of the content off their site. At this point while they aren't doing full blown peer review, they are putting a lot of work into providing first pass moderation that ensures the content in their academic categories is of at least some level of respectable academic quality.