Why does LPX download the sound library?

My understanding is LPX and MainStage share the same sound library.

Move Logic Pro X and MainStage content - Apple Support

However, Logic is currently downloading 58.25GB. When I check MainStage the complete sound library is already installed.

How to I check to see if the libraries are in fact being shared?

I have not relocated either library. They are installed in the default location.