The problem is, some information is interesting only to a tiny audience long after the fact, so there's no chance anyone would've thought to curate it in the moment. E.g., for a few of my projects I like to dig up old versions of niche libraries to observe how their behavior has changed. But for most traditional distribution methods (putting the tarball up on your website or on a SourceForge-style website), the common assumption is that no one wants old broken versions, so you can regularly wipe everything but the last 1-3 versions to reduce clutter: the consequence is that the old versions accidentally saved on archive.org may be the only copies left anywhere. The more recent practice of publishing Git repos has considerably improved this situation.