From my perspective, there are a few reasons why Staff Submissions are still a thing:
[spoiler=Staff Submissions]
1. Community Input
It's always important to heed what the community has to say about something, whether it be in regards to a rule change or new Staff Member(s). Reason being that it introduces a third party to provide their input on the matter; an outside perspective that may differ from that of a Higher-Up's. It also gives players/users who only have Member status a chance to give their input on something that may very well influence the Servers (or even clan). In other words, it gives the 'Member' rank an important air around it whereas a 'Registered' user's input wouldn't be as influential. Such is the case with every other form of application/protest in terms of 'Member' influence.
2. Inadequacy/Shortage of Staff
During times where the Staff pool is shallow, the application process becomes crucial in boosting those numbers. It allows Higher-Ups to specifically monitor potential applicants as opposed to having to determine who is deserving of a position. It also eliminates the potential of a player declining the offer to become a Moderator/Administrator as an applicant wants to have the position. This can really cut down on the time it would take to promote new Staff since not only would there be community input to aid in developing a portfolio of the applicant, but as aforementioned, the Higher-Ups can eliminate one step (finding potential applicants) which can take anywhere from a few days to a week or more. Long story short, it [potentially] cuts down on the time spent trying to find new Staff.
3. Establishing Interest in Player
There are times where players who have an extensive knowledge of the Server rules slip through the cracks and are never really noticed by the Higher-Ups. However unlikely, this is bound to happen, and when it does it makes these applications a chance at getting that player's name out there. Even if that player's application is denied, it still gives the Higher-Ups an option down the road should they be lacking in Staff.
4. Extra Income
This one is a given, it's what we're all discussing at the moment. Every little bit helps, even if it's a "donation" of $5 toward gaining the ability to post a Staff Submission.
In the end, having the option to submit an application is better than not having the option at all; even if players are inclined to "donate" (still really think this should be considered a fee).
That all being said, I brought this up in a comment and I'm interested to know whether Paid Moderator/Administrator positions are still a thing @Rhododendron . If so, I recommend an addition of it be made in the "Moderator Submission Rules" thread (maybe a discussion had on whether it should still be a thing or not among the Higher-Ups; and if so whether it should have some sort of rules).
Also still curious on a before/after of the Moderator Rules, honestly can't tell what is new and what isn't.
EDIT: Also noticed that the rule on "donations" was reworded which is great, but it is still hiding the fact that you have to donate in order to post a Staff Submission in the first place ("weighing favourably" is like saying "it wouldn't hurt to", but it is actually necessary in order to post a Staff Submission to begin with and may confuse Players/Members). *Note: This is assuming that Players are still unable to actually post a Staff Submission, if they are able to now (non-donators now have access to the Staff Submission form), then please disregard this edit.
Another EDIT: Hate to be an annoyance, I know this post is long enough as it is, but for the record; if a Higher-Up could post what they've changed or included in threads like the "Moderator Rule" one, it would be greatly appreciated as opposed to just making an edit and expecting everyone to know about it afterwards without little to no warning or announcements.