> you just have to do maintenance through manual find-and-replace now

Do you? It doesn't seem even remotely like an apples-to-apples comparison to me.

If you're the author of a library, you have to cover every possible way in which your code might be used. Most of the "maintenance" ends up being due to some bug report coming from a user who is not doing things in the way you anticipated, and you have to adjust your library (possibly causing more bugs) to accommodate, etc.

If you instead imaging the same functionality being just another private thing within your application, you only need to make sure that functionality works in the one single way you're using it. You don't have to make it arbitrarily general purpose. You can do error handling elsewhere in your app. You can test it only against the range of inputs you've already ensured are the case in your app, etc. The amount of "maintenance" is tiny by comparison to what a library maintainer would have to be doing.

It seems obvious to me that "maintenance" means a much more limited thing when talking about some functionality that the rest of your app is using (and which you can test against the way you're using it), versus a public library that everyone is using and needs to work for everyone's usage of it.

> If you're the author of a library, you have to cover every possible way in which your code might be used.

You don't actually. You write the library for how you use it, and you accept pull requests that extend it if you feel it has merit.

If you don't, people are free to fork it and pull in your improvements periodically. Or their fork gets more popular, and you get to swap in a library that is now better-maintained by the community.

As long as you pin your package, you're better off. Replicating code pretty quickly stops making sense.