Proguard obfuscation, particularly when you get to aggressive renaming (there are a lot of valid characters for a java class or method), flattening, overloading and inlining, can make it very hard to understand what is actually happening.
Its great to make this step.
minecraft had none of these, it only had clean and predictable name obfuscation.
Super interesting to know. I wonder why they bothered!
Thanks for the info.