I think you're missing the part where academics still submit to these journals and conferences just like everyone else. They just also put it on ArXiV or theri

I think you're missing the part where academics still submit to these journals and conferences just like everyone else. They just also put it on ArXiV or theri own website at the same time or sometimes before publishing in the bigger journals. The majority of journal copyright agreements allow authors to post the article publicly if they choose.