Mojang/Microsoft actually releases obfuscation maps for Minecraft: Java since 2019. This maps the decompiled random class names to the official variable/class names used by Mojang devs.

In an effort to help make modding the game easier, we have decided to publish our game obfuscation maps with all future releases of the game, starting today. This means that anyone who is interested may deobfuscate the game and find their way around the code without needing to spend a few months figuring out what’s what. It is our hope that mod authors and mod framework authors use these files to augment their updating processes that they have today. These mappings will always be available, instantly and immediately as part of every newly released version. This does not, however, change the existing restrictions on what you may or may not do with our game code or assets. The links to the obfuscation mappings are included as part of the version manifest json, and may be automatically pulled for any given version.

https://www.minecraft.net/en-us/article/minecraft-snapshot-19w36a

As others have said, Java is pretty easy to decompile, so there were community maintained obfuscation maps before (huge amount of work).