Everything else they might do - collating papers into a physical journal, complaining about bibliography formats, etc. is superfluous nonsense that nobody really cares about.
Look at arxiv - the only thing it's missing that journals have is reviews.
Yelp -- How are their costs significant? Web hosting is extremely cheap.
Twitter -- How are their costs significant? Web hosting is extremely cheap.
Is the value of journals over arxiv worth the price? (market says yes, but markets are sometimes wrong).
https://arxiv.org/help/support/faq#2B
https://confluence.cornell.edu/display/arxivpub/arXiv+Budget...
Or SciHub's, for that matter.
But this is one of the biggest sites in the world. Something closer to what Journal Publisher's would need is Arxiv.
Arxiv's budget is $1m of which they spend $60k on hosting and basically all of the rest on staff and staff support.
Eslevier's revenue is £2.5b. billion. Their profit margin is over 50%. What a monumental waste.
That is a pretty significant difference.