A good example for generated code are typed clients for an OpenAPI interface. Instead of writing a REST client on your own based on a spec, you generate it. And if something isn't right in the first place, don't edit the generated code, fix/configure the generator instead!

Or database models. Either generate the database from the models or the models from the database.

That's exactly the problem. and because templates allow you to modify the code, the template creators do no work on generalizing it so it covers all the use cases. So, on practice, templates usually require that you modify it.

And now you have a huge codebase, mostly with the default text, but with some changes at random, and one of those changes is breaking it. Good luck finding it.

Sigh... every time I see people generating any code (say through external tool or through IDE) I am always thinking how this could be a simple macro in any Lisp language.

So if you need a lot of template code, then your design or your framework is not well suited for the task.

In software development the goal is usually to move commonly used functions or patterns into a library or a framework, instead of copy&pasting them with slight modifications.