It is site practice to delete unsupported answers
Admittedly it's never really documented/discussed on it's own, but mostly in the discussions around fun topics like game recommendations and designer intent requests. Specifically, when the questions type really needs supported answers, aren't getting them, and we need to talk about how to moderate them.
But it does also show up in other guidance: What are the citation expectations of answers on RPG Stack Exchange?
We don't want your opinion; we want your expertise. If you do not have experiences you can bring to the table in that particular case, do not answer the question. Answers not doing so may be downvoted and/or deleted.
(It talks about experiences as citations because it's from the section on subjective questions, however I see no reason to distinguish the two on this other than what type of support the answer needs to bring.)
But haven't we got a post notice for this?
Yes, there's a post notice for needing citations, but post notices are a poor tool for moderating content. They are fixed wordings and only available to a very small subset of users. Comments are better at pointing out problems because they are customizable (by default you write out each one) and availible to many users. The post notice does also not exclude deletion, but explicitly warns about it:
Want to improve this post? Provide detailed answers to this question, including citations and an explanation of why your answer is correct. Answers without enough detail may be edited or deleted.
Let me try to explain why that post notice get used at all, if those answers should get deleted. Firstly, deletion might not be the correct thing. If the answer is probably salvageable, users should get a chance to edit it, or comment for the poster to do so. Also, diamond mod deletions are instant, and harder to revert (can't be undeleted by non-diamonds). There's also an important learning and healthiness aspect to community doing moderation and evaluations, so we often try to not immediately delete (nor close, etc.) borderline cases.
So, we prefer to let the low quality review process do its thing. We might flag the post (if it wasn't already), add a comment with out concern (again, if it's not already covered), and add the post notice for increased visibility of it (if we remember to/think it's worthwhile). Expecting the post notice to be used beyond this is putting an aspect of site moderation too much onto the diamond mods, I hope you want us to put our efforts into more useful things.
So for the specific answer
Without support being added to it, I don't see it having any value. And it being deleted does not prevent the poster (nor 10ks I believe) from editing it. The user could then vote to undelete and/or flag for undeletion (if diamond deleted, as this one retroactively is, the flag is necessary). No such efforts have been made on this answer. I don't personally see the reason to undelete it, but I'd be happy for someone to change my view on the quality of an answer at a score of -6.