Minor nit - "the full java version of an at-least 8 years old release" (which is necessarily missing -a lot- of what people would consider "Minecraft" these days.)

Minecraft these days is missing a lot of what people would consider "Minecraft" 8 years ago.

I don't get it - isn't this blatant copyright infringement? Seems like they're just running some kind of cracked Minecraft build with a JVM-in-JS layer or some such trickery?

yeah, it's JVM-to-wasm plus an lwjgl-to-webgl library plus various compression packed into a single .html file