Why not Cache from Intersystems?

I have some experience with a very large OLTP system that is 7+ TB in size and performs very well for 30K+ concurrent users.  It is built using Intersystems Cache based on the very old but very scalable MUMPS platform.  Why don't I see more discussions about archiectures such as these in this forum?  I am curious why this platform scales so much better then the typical RDBMS.