I've asked the same question and still haven't got a concrete answer as to why anyone would use devcontainers.

As I understand it, devcontainers use some base image and then instructions in json file with steps what to add for that specific app. Why not just make a docker image with everything your app needs and use it?

This sounds better if you never use cloud editor platforms; devcontainer can be useful if you jump between local coding and say GitHub Codespaces where devcontainer.json is automatically recognized.

IME a hybrid of your approach and devcontainers works best in that situation though, because I don't want to rely on or even figure out how to use the devcontainer recipes, and building them every time the thing spins up takes forever. I like a workspace container defined in a Dockerfile that publishes to a registry and a very basic devcontainer config to use it.

I think a lot of it is ide integration. You can see devcontainer details in a tab in vs code for example.

But I think the biggest thing is code reuse - there are a lot of plugins for dev containers so it is easy to spin up a new project with things like git, node, defining users, etc etc

IDE integration. For example, I use the Jetbrains RustRover IDE on Fedora Atomic, which is an immutable Linux distribution that is based on keeping the OS setup as clean as possible. I use DevContainer to install the toolchains I need for my project and the IDE takes care of setting up my development environment.

I imagine that is a bit tricky to optimize for build speed on a monorepo. Say you have 3 things to build you need to pick the order OR you could use multiple targets amd copy stuff around I suppose.

Is the debugging experience good?