Yeah mods are just regular Java .jars that can do anything. To circumvent this issue Mojang introduced datapacks but they are super limited in what they can do. They’re basically just Minecraft commands in a file along with some manifest files to change e.g. mob loot drop rates. These Minecraft commands are Turing complete but a huge PITA to work with directly, no concept of local variables or if statements, no network access, etc. Every entity in MC has associated NBT data that is similar to JSON that stores values like position, velocity, inventory, etc. You can change NBT with commands for mobs, but in what can only be described as a religious decision, Minecraft commands are unable to modify player NBT. So for example it is impossible to impart a velocity on a player.

One wonders why Mojang didn’t embed Lua or Python or something and instead hand-rolled an even shittier version of Bash. The only reason MC servers like Hypixel exist is because the community developed an API on top of the vanilla jar that makes plugin development easy. Even with that there is still no way for servers to run client-side code, severely limiting what you can do. They could’ve easily captured all of Roblox’s marketshare but just let that opportunity slip through their fingers. Through this and a series of other boneheaded decisions (huge breaking changes, changes to the base game, lack of optimization), they have seriously fractured their ecosystem:

- PvP is in 1.8 (a version from 2015) or sometimes even 1.7 (from 2013)

- Some technical Minecraft is latest, some is in 1.12 (from 2017)

- Adventure maps are latest version

- Casual players play Bedrock (an entirely different codebase!)

The words “stable API” have never been said in the Mojang offices. So the community made their own for different versions, servers use the Bukkit 1.8 API, client 1.8 mods use Forge, latest mods use Forge or Fabric. The deobfuscated names are of little utility because the old names are so well ingrained, and modders will also probably avoid them for legal reasons.