Why engine modules aren't shared between programs?

When the build tool builds the engine it creates a separate version of the same module for each target so we get for example UE4Editor-Core.dll, ShaderCompileWorker-Core.dll etc. Why is that so? Well I can assume that these versions are different, have different optimizations etc. I can certainly see that it makes sense when building a shipping game for example, but why can’t the editor and development programs share modules?