Well, actually it can be. It just takes a lot more to decompile code than compile it. Depending on the objective accuracy.

Example: the Super Mario 64 Decompilation project. This was a project that used various debug data that was left in the rom to decompile the game back to a source code that compiled a byte accurate version of the rom. This took about 3 years and a lot of skilled developers to accomplish.

Side note: Super Mario Bros wasn’t built using a compiled language, but rather Assembly. So technically that would be a Disassembly not a Decompilation.