I like your argument about sustainability. With proper free software, the code itself is part of the product. When you're left to work on a binary, it's not even not guaranteed that your patch won't work with the next version or whatever - often the authors specifically make the life of the modders harder. It's part of the product that you don't get to modify it. It's signed, obfuscated, there's checks for integrity, uglified, ABI modifications for the sake of breaking compatibility. So much of the effort is just fighthing against that, and that's a directly opposing sustainability.