So, especially with PC games, software is compiled using an IDE/language and runtime environments. That last part is why games stop running on newer versions of windows, and it's especially why older games can't just "be ported" to consoles, mac, etc. Once you compile a program, it's like etching that program into a stone called an executable/extension(DLL). If you want your program to run on anything other than the old compatible hardware using their runtime libraries, you gotta have the OG source code in order to recompile. Blizard North had a liquidation sale way back and the source codes to their projects was in it. They've been scrambling to get it all back to make remakes/remasters.