My guess is that it's much easier to keep the story straight-to-the-point in 1st person. It might also be more favorable when there is a 25K char limit ---- meaning almost every sentence needs to advance the plot.
I do think 3rd person has some advantages:
(1) Maintains objectivity: It helps preventing the writer from injecting too much of him/herself into the protagonist to mess up the pacing. This helps when the plot becomes emotionally heavy.
(2) Provides flexibility: 3rd person allows asymmetric information scenarios, where you the reader knows that A knows something that B does not know, but B knows C knows D knows A knows something. Okay, I'm babbling, but you see how fun writing and reading can both be, if the writer knows how to utilize this. I myself am still learning about this part.
(3) Opens the story to a wider audience: A female reader could subconsciously find it hard to relate if the "I" in the story was straight up male, and vice versa. I'm confident you can infer what other examples might be.
Writing first person is one the most difficult ways to do the thing, in my opinion. You really want the character to be special, interesting, attracting on many different levels if you want to make a first-person story good.
First of all, not every character would make a good narrator or storyteller, whilst the auther may be tempted to throw in a couple of juicy words and constructions to flex on. I don't think that a contrast like this leaves readers with a good impression.
Second, the information available to this character regarding other people, events, places, whatever is limited, and when it's not as limited, it may get way to close to Mary or Martin Sue territory. Doesn't do your story any good either.
Lastly, if done right, first person narrative can be incorporated into a third-person narrative quite well if done right. Strugatskie (russian/Soviet sci-fi authors) did a good job on this in their
The Doomed City: the narration was third-person for the most part, although there were multiple sections where one of the characters had an internal monologue that was NOT separated from the narrator's text with quotes or anything. Surprisingly enough, that felt fluid because the emotions of the narrator felt similar to the character's closer to the monologue. They sort of collaborated, which really facilitated readers' understanding of the thought process and emotional state of the character. Another example is a wild one, but it comes from the same authors:
The Ugly Swans is a story that is kinda written by a character (an author) in another book of theirs,
Limping Fate, yet both are real tangible stories written by Strugtskie (I had a book with both stories,
Limping Fate was told in odd chapters,
The Ugly Swans was told in even chapters, that was pretty neat).
However, first-person is actually great for short stories that you don't want or plan to invest a lot into. It allows you to tell a story without that feeling that you're doing something wrong with all the repeating pronouns and names and euphemisms for the same character, you're allowed to drop some details due to the character's limited knowledge, and the story isn't likely to feel naked and lacking details because of that. Still, 25k characters should be enough for a third-person story to unfold sufficiently if you don't give it too many elements to cover, though.