It didn’t require zero lines of code. It required a huge amount of backend code to set up the abstraction and make lots of built-in types that adhere to the abstraction. And in cases when the abstraction fails to offer the exact type of extensibility needed (which is most of the time unless you’re authoring yet another highly abstracted library that can tie its use cases to that underlying abstraction, which is never in practice), then it was wasted effort, and “no overhead” is a false description, because you still have to dig into the guts of all the stuff that gets auto-generated if you plugged into the abstraction and change the mechanism of how it gets auto-generated for your special case, or else (usually easier), just write separate data structures outside of the abstraction vortex and have a few small converters or helpers that marshal your custom data type into and out of the abstraction for the really tiny anount of auto-generated features that actually matter to the use case.

The “but it requires zero lines of code” thing is so misleading once you hit real use cases where the choices of how the abstraction auto-generates things end up being unusable for some specific situation.