Whenever I tried interacting with mailing lists in the last five years, I always needed to subscribe or wait for days for someone to moderate the spam queue.

Anti-spam measures are a large part of what made using MLs so annoying. From a moderation side, MLs are more work for that reason as well - Github and Gitlab at least get rid of spambots shilling shady cryptocurrencies, weenie enlargeners or questionable quality designer drugs. With MLs, all of this ends up in your moderation queue as well.