I don't understand why people think tales of pizzaplex is 100% canon and not just parallels

Back then silver eyes trilogy reveal purple guy name as william, and confirmed it in sister location. No one gonna say silver eyes trilogy is 100% canon

So why the fandom think tales of pizzaplex is 100% canon just because it's tell story about the mimic?

Edit : i kinda agree with one of the replies that say tales of pizzaplex exist to fix the mess that steel wool did in security breach, and confrim what is scott idea and what is not. Because we all know when developing security breach scott only give the big story and let steel wool add the rest, so this is his way to fix that