They never tried to stop it but they never fostered it either. It was just coincidentally easy to reverse engineer the code and install mods. But the interfaces

They never tried to stop it but they never fostered it either. It was just coincidentally easy to reverse engineer the code and install mods. But the interfaces were VERY brittle, and mods had very specific version requirements. Official mod support (with an installer and an API) was on the dev roadmap but never materialized.