Literally why? They tried this shit already and it went over like a wet blanket.
I think this also highlights a general high-level problem with the American media industry. They’re never satisfied to just let something good stand on its own, every success needs to be milked until they’re no longer profitable, regardless of whether or not there’s actually an idea for a good story to tell. The Japs at least have the decency to mostly limit their moneygrubbing to gacha games, figures/statues and non-canon high school spin-offs instead of tainting the main property with garbage sequels.