One reason that domestic shipping cost is so high is that 1920 Jones Act[0] prohibits shipping between US ports with non-US ships. This drastically reduces competition and increases prices. Hawaii are particularly hit by this, with estimate $1800 per year per family in extra cost [1].
[0] https://en.wikipedia.org/wiki/Jones_Act_(sailor_rights) [1] https://www.wsj.com/articles/jonesing-to-give-up-russian-oil...