A humanless MonsterVerse film wouldn’t be cheap to make. A film that heavily relies on CGI would cost over $400 million to create, and from a business standpoint, it wouldn’t really make sense for Legendary to invest that amount of money into a film that, to be honest, wouldn’t be a guaranteed critical and financial hit.
Considering how every MonsterVerse film has made less than $570 million USD so far, how likely is it that a MonsterVerse film with minimal or no human involvement in the story would make as much or more money than that? I’d say it would be a film that would either make or break the MonsterVerse, even if Kong were the main character.
Peter Jackson’s King Kong only made $562.3 million USD, which is slightly less than Kong: Skull Island, which made $566.7 million USD, and look at what that movie had going for it: it was a remake of an iconic monster movie from 1933, featured stellar motion capture technology that gave the titular monster a tone of personality, was made by an acclaimed director who just got off of finishing his successful Lord of the Rings trilogy, featured a lot of great actors such as Jack Black, Naomi Watts, Collin Hanks, Kyle Chandler, Adrien Brody, and Andy Serkis, and you can argue it had a lot more going for it in terms of its story than Kong: Skull Island.
Even though it did really good, it didn’t do amazingly at the box office. It made about the same amount of money as the MonsterVerse films. So what are the chances of a MonsterVerse film with no human characters in it making as much or more money than that? It’s not a guarantee.
And just because we as Kaiju fans see the Titans as characters and connect with them on a deeper level doesn’t mean general audiences would do the same. Since Kaiju fans really connect with the monsters, they’d be more naturally inclined to see a movie where they are at the forefront and the humans take a back seat. But Kaiju fans only make up a minority of moviegoers, while the general audience is the majority, and because they are in the minority, they wouldn’t bring in enough money to make the film a financial success. The general audience is the audience who Legendary needs to make their films successful. But because general audience members have always had a stigma towards Kaiju movies and just see them as mindless entertainment, they probably wouldn’t be interested in seeing a Kaiju movie that only has monsters fighting and converging the planet. Therefore, the film wouldn’t be a financial success. I doubt it would be a critical success either since critics didn’t like KOTM due to the human drama. So if they didn’t like a film that featured Toho’s most iconic monsters and some great monster action, what are the chances of those same critics praising a film with only that and no human characters? Once again, it’s very unlikely.
If Legendary is interested in telling a story that features the monsters as the main characters, they should either make it into a graphic novel series or a straight-to-Netflix anime with a reduced budget. I think it’d be cooler if they made a Titan War anime since animation is a great art medium to tell a story that has minimal dialogue and is on such a large scale. Animation would also allow the Titans to be more expressive than they would be in a real-world feature film. And hey, we’re getting a Skull Island anime, so why not make one about the Titan War if it ends up being successful?
TLDR: Even though a humanless MonsterVerse movie would certainly be ambitious, it just wouldn’t be a guaranteed critical and financial success. Therefore, it’d be smarter for Legendary to make humanless content on a smaller scale.