There are two primary issues. In game development, for developing game features, iteration speed is the most important factor, you usually want a higher level scripting language in your game engine, so that a developer's workflow looks like this: make a simple change, hit a reload button, issue a few inputs, go back to the editor, make a simple change, repeat. Other popular game engines, more or less, solve this problem by providing a way to make gameplay features in a higher level language (GDScript in Godot, C# in Unity, BluePrints in Unreal Engine, often Lua with custom game engines), with Bevy, you make a change, and you rebuild the code, and often times, making a simple gameplay logic change (for a spell, an item, or some NPC interaction), will also change the ownership rules in case of Rust, because you may want to now access the same item mutably in two places or other things, and that requires you to restructure your simple script to appease the borrow checker, which also brings us to the second issue, in game development, a lot of bad practices, become good practices, take cyclic references for example, which are a common pattern in video games, in other lower level languages, or languages that allow embedding a higher level language, it's not that big of a deal, in Rust you have to do some shenenigans with things like RefCell<Vec<Rc<RefCell<Item>>>> which is simply not very ergonomic and adds a lot of development friction. A lot of people don't realize that game engine and gameplay programming are two vastly different things that have different requirements, and Rust is a poor fit for the latter.