That it can be distributed, and that there is source available for modifications, expansions, and ports to modern systems.

Generally game assets don't depend on the external environment like code does. Sure, porting is still a lot of work (which I don't think has been done for this one), but it's less work than porting an arbitrary executable.

But most importantly, not everything has to be a product with a practical benefit for the user, if the project goal is to be able to be a drop in replacement for all the code, and it does it, and the people involved are fulfilled, that is perfectly enough.