Buildpacks have been in the industry for many years (thanks to cloud foundry) but it doesn't really scale. For simple things, sure they are good enough but more often than not you want to your application to be packed in a special way and you end up putting more efforts than using simple Dockerfiles

You can always start from the generated image (which contains the steps used to build it) and extend it in your custom Dockerfile if your project gets so big, right?

This was definitely true of previous generations, where each buildpack needed lots of magic to play nice with others and you needed to fork them if you wanted a particular feature.

CNBs are easily composable, partly because of that experience. No more forking necessary.

This is especially true of Paketo's buildpacks, which tend to do exactly one thing each. E.g., Paketo Node.js buildpack is just a configuration file that's composed of other buildpacks: https://github.com/paketo-buildpacks/nodejs/blob/main/buildp...