So here is the thing about leaks especially ones that pertain to source code, for the most part they are not very useful for projects and are more so treated as easter eggs or something to collect. Code, much like games, is copyrighted and therefore unauthorized distribution of it can put you into legal trouble. Therefore if copyrighted code is leaked, legally no one unauthorized is allowed to have access to it. Meaning this source code leak cannot be used to help run the game on other platforms. But technically that is a lie because there is a term known as "cleanroom programming" where one entity would focus on making the actual code while another entity would have access to the unauthorized software but only guide the other entity if they are heading in the right or wrong direction. Some people argue that even that is not safe enough but either way, having the source code being leaked does not help in the long run.
tl;dr There is a big difference between source code being made publicly available and leaked from a legal perspective.