Warning! Spoilers ahead for Star Trek: Section 31.
First of all, I must clarify that I don't believe anything creative like a movie can truly be considered a "failure." Any piece of art ultimately is what it is, and our individual tastes can play a big role in whether or not it works for us. Even if something doesn't meet anyone's tastes, it's still a learning experience, at the very least. In that way, Star Trek: Section 31 is an excellent learning experience.
Section 31 is…boring
Some movies are corny or "bad" in ways that are actually charming or fun to watch. Other movies aren't universally beloved but manage to elicit emotions from the audience by making them mad at the films. Those may not be the receptions the makers of such films would have liked, but at least there are reactions. Section 31, by contrast, has the distinction of just feeling pointless.
The characters have no goals, so there is no plot
To illustrate what I mean here: In The Wrath of Khan, it is established early that Kirk wants to avoid confronting his age and mortality and that Khan wants revenge against Kirk. The plot proceeds from there. In the end, Khan is defeated, but Spock dies. Kirk won at the cost of his best friend. The audience is engaged from the start and left with the same bittersweet feeling Kirk has at the end.
If I were to describe the "plot" of Section 31, I would have to simply recount the various events that transpired in its 95-minute runtime. At no point is it clear why any of the characters are doing what they are doing, and San, the "major" antagonist of the film, doesn't explain his reasons until the end of the movie? In the end, it is unclear whether the team actually won or not.
Of course, Section 31 should not imitate Wrath of Khan (nor should other Star Trek movies), but it needed to clearly define the characters and establish their objectives. In doing so, the story would be comprehensible and compelling to the audience on some level.
Filmmaking basics
If Section 31 struggles on the character and storytelling end, it doesn't help much in the actual creation of the film either. A mixture of careless cinematography, unmotivated editing, and indistinct production design makes it an unremarkable chore to watch.
Cinematography
The camera work in Section 31 comes off as an amateurish attempt to make things look "cinematic" for no reason. Compositions waste the ultra-wide aspect ratio by centering everything in medium shots, and the endless camera movement is distracting.
Editing
In Section 31, the editing is haphazard in a way that makes the whole movie feel rushed. The audience never really gets a chance to process anything that happens, and excessive quick-cutting makes it seem like the main goal of the editor is to keep to that 95-minute runtime.
Production design
Section 31 was trying to be a "different" kind of Star Trek, but seriously, none of the sets, ships, or costumes give any indication that this is Star Trek. Aside from a few secondary alien characters and smartphones-as-tricorders, the whole movie looked like it came from the Generic Sci-Fi Movie Catalog. Even if it isn't Star Trek, a sci-fi movie should want to be visually distinct on some level, right?
Wobbly filmmaking can't hide a nonexistent story
The original Star Trek continues to gain new fans, despite its dated production design and effects, because it has a cast of endearing characters with plenty of solid-to-great episodes to make up for its handful of actual duds. Section 31, by contrast, has undefined characters meandering around a plot in an indistinct sci-fi setting.
If I were to "fix" Section 31, I would try to make sure Georgiou's goals were clearly defined. Then, I would work out the goals of the other characters. From that foundation, a coherent plot could be constructed. This clarity could then allow for thoughtful, creative decisions at every other stage of the film's creation. Section 31 exists as it is, though, and in that way, it's a great learning experience.