My favourite ecosystem simulator is Rain World, and trying to put that kind of creature interaction into a sandbox game just seems... unfeasible. Rain World is a game that uses static maps, so the creature AI is then able to navigate however it wants over the pre-defined collision. In a game like Vintage Story, not only is the world randomly generated each time, but the player is able to change it however they want. More complex animal AI would need them to have knowledge of the terrain, specific spawn/territory nodes, and other stuff that just seems like it would break constantly.