The Minetest API is itself a bit more primitive, as it's server-side-only Lua scripting as opposed to essentially hacking the whole game engine inside out with

The Minetest API is itself a bit more primitive, as it's server-side-only Lua scripting as opposed to essentially hacking the whole game engine inside out with zero security involved. As for modpacks, they add a lot of RAM usage especially to the whole thing. Minecraft 1.9 also made it possible (theoretically, that is it's possible in the code and probably used by Realms) to run multiple servers in the same Minecraft server instance, saving a lot of overhead on the block definitions, classes, JVMs, etc.