The large number of approvers is specifically because the rules are stacked heavily in favor of approving something (one random approver that likes something can overrule every other approver hating it) and they are explicitly told to be completely subjective in what they approve. As has been argued many times before on these forums, approvers are a ring species that have developed around specific tastes in a system that overtly encourages Eternal September, explicitly incentivizing territorial behavior. If you look at the comics on this site, you'll see the same four approvers approving absolutely everything, and there are some approvers whose names I only see when attached to some of the porn I had explicitly marked as "poorly drawn".
I, personally, go through every uploaded post and will try to apply quality standards, although there certainly are things I don't like and will judge more harshly, but with that said, there are even filters you can apply to the mod queue to make it so you don't see any post that doesn't fit certain criteria. Between "only approve what you like" and that, you can see some real differences in what approvers will approve. Considering some wild variance in how often different approvers actually log on, you can get some notable differences in what quality is approved just by when approvers with lower standards are active.
And yeah, because of that, I've apparently gained one of the highest rates of approvals among approvers, and I generally have been good about going through new additions every day, so it's not that things go unnoticed, it's that I find reasons not to approve things.
Keep in mind that even if something looks good, there may be other reasons not to approve something. It may be tagged as a sample, it may be a really detailed official art that has really terrible jpeg artifacts from someone doing horrible compression ripping it from the source, the uploader may have screwed up uploading or tagging somehow. There's also the whole anatomy thing, where there's reason to hold off on approving something with questionable anatomy.
And Iridescent Slime is right - there are more things in consideration than flat artistic skill, alone. Sweetpea likes to talk about it in terms of a point scale, where if an image winds up with a positive score, it gets approved. So you start with a score from artistic skill, then add or subtract points for different things like bad anatomy, good composition, and whether or not the image actually manages to be entertaining in some way, and the overall score determines whether you approve it or not. This post, for example, was likely deleted in spite of being technically passible because it's just the same character about which we have plenty of pictures just standing there in front of a blank white space. This post, however, has the character actually doing something in a setting with actual context that makes it more amusing and worthwhile as something to look at while already browsing images of that character. This post, meanwhile, is a fine art parody, which makes it amusing enough that I'd approve it in spite of having some awkward art style. (Not that I had a choice in that one, it was uploaded by an unlimited uploads user.) Likewise, I will approve comics of much lower artistic merit if they're funny or tell an interesting dramatic story because those elements will add a significant positive score to counterbalance the negatives of generally hastily-done artwork.
As said before, however, there are real differences in how people weight these things, so you'll wind up with some approvers approving basically all the comics on the site while other approvers seem to hate the fact we have comics at all.