Unfortunately art quality is subjective, which means the only way to discern whether a post is "good" is to show it to a lot of people and see if they agree. In the case of danbooru, we go even further by only requiring a single approver among the dozens we have to approve a post before allowing it in the main gallery.
However, this goes the other way as well: if not even a single approver likes a post, then it's hard to justify its presence. Sometimes posts get missed, but it's rare and that's what the appeal function is for.
To get to your question, think about it this way: we want to incentivize good uploads, which we define as uploads liked by at least one user among the many ones granted approval privileges. The dynamic upload limit exists for this reason: the more an user uploads posts that are similar in quality to the existing gallery, the more they're encouraged to upload, through the unlocking of more upload slots (and eventually unrestricted privileges).
If there was no penalty for uploading substandard posts, or if there wasn't an immediate reward in uploading well-liked posts, then someone could just flood the site daily with a lot of mediocre uploads without any motivation to improve. This is exactly what used to happen with the old upload system. In fact, even now there's several users I can think of that just won't improve in terms of upload quality and keep uploading a relatively high volume of posts that skirt the line of acceptable quality. I think it would be much worse without the current restrictions. Look at status:deleted and you'll see what I mean.
As for the disapproval options, those are used rarely and only for the worst posts, because most approvers can't be arsed to think too much about a quality of a post, and truth be told it would be unreasonable to ask of them to pass a detailed judgement on thousands of posts a month. If there was no penalty for posts that were just disapproved for nobody liking them, then I'd bet a good 95% (or close to that) of submitted posts would cause no penalty on deletion.
The only advice I can give you is to try and be more selective on what you upload, and try to aim for unrestricted privileges so that you'll then be able to skip the queue without worrying about something being too niche or an art style being too weird for approvers' taste.