Board Thread:General Discussion/@comment-1031724-20161020032419/@comment-477304-20161021210821

Sonic didn't exist then. Shadow was Gerald's only option as far as he knew.

And that's because they're most likely dead. The "never found the body" trope does give them weiggle room if they really wanted to bring some of these guys back, but I doubt they do. Eggman Nega's probably the most likely to appear again because he wasn't even shown to be mortally wounded.

Metal Sonic, on the other hand, isn't dead at all for multiple reasons I've already gone over.