Minecraft servers can't hold half as many people as a MMO can.
The only wild exception being Hypixel's servers, which are nearly MMO capable. But they perfected channels, and multi-server linking that MMOs do. They still do lag more than most MMOs, but Java isn't an optimized language for that sort of thing. Despite Runescape using Java originally.
Also, the Windows 10 version of Minecraft doesn't use Java, it uses C / C+ / C#