yarn workspaces lays out node_modules in several directories, nested with your source code. It relies on node module resolution semantics of looking for a node_modules in parent directories when a dependency isnt' resolved

Bazel-managed dependencies are in a single node_modules directory that's outside the source code.

We could have multiple bazel-managed node_modules, but would still need each of these to be a complete copy of deps needed for a given binary to run.