Domen had a bad time using B2 for Cachix and had to migrate off it. So I wouldn’t be surprised if people are nervous about it.
AIUI (I don’t have any decision-making capacity here), deletion is on the table but needs to be handled carefully, because this bucket might have the last copy of sources that no longer exist. I know this has already happened because I found some instances when testing fonts in nixpkgs for reproducibility.