The answer is mostly a mixture of "we need to properly establish policy and right this moment the site owner isn't around enough for that" and "we're only fuckin' humans, okay?"
And also do you have any idea how much work cleaning up the e621 senseless hyperactive tagging *actually is*? We can't just ban or alias all the high-order tags we don't like such as, say "electronics" or "furniture", because there are pics where such tags are relevant (though not that many), but we otherwise don't want them on every gotdam pic with a random television or a cell phone in it, and there lies the problem (similarly with tags for the basic body parts like "fingers" or "genitals").