Most code has type annotations but we don't enforce it. A lot of code was written before typing became well supported and we never went back to add it to every

Most code has type annotations but we don't enforce it. A lot of code was written before typing became well supported and we never went back to add it to every old piece of code, we add them when people touch related code sections. Typing definitely makes it a lot easier to navigate the codebase. But in the end maintaining any large codebase is a question of discipline which starts with simple things like code layout, class and function names, isolation of functionality.