Speaking personally, I'm not really sure what Sony Pictures hopes to accomplish with this.
My guess? They're planning to torpedo the live (Sony-produced) films completely. They'll need the animated films because - if they don't use the license - they lose it and the rights revert to Marvel.
The film, which is currently slated to hit cinemas on July 20th, 2018 will be produced by Phil Lord and Chris Miller. Moviegoers may remember the duo from their work on The LEGO Movie...
As others have pointed out, animated superhero films tend to more faithful to the source material. There are a lot of reasons for this, but my theory is that the biggest reason is that superhero films fall into the Hollywood "blockbuster" bucket. The directors picked by the studios for blockbusters generally have huge egos and believe they are a lot more creative and talented than they actually are. As a result, they absolutely believe they can "improve" on the source material by shitting all over it. The latest Spider-Man movies are an excellent example of this, but also see Michael Bay's
Transformers,
Man of Steel, every Fantastic Four film ever made, etc.
Animated films, on the other hand, typically have directors who are (a) more humble; and (b) more likely to have a personal connection to the comics. While animated films have more modest budgets, they aren't as limited by technology and the laws of physics as live-action films and can have incredibly elaborate set pieces that would be prohibitively expensive for a live-action film.
Getting back OT,
The Lego Movie was brilliant. My guess is that Lord and Miller approached Sony about this project. Sony may be run by idiots (evidence suggests this is the case, anyways), but even an idiot can see that this looks like a home run. Why wouldn't they approve a proposal like that?