system
Given the following post, respond as if you're commenting on Reddit:
human
[Scooby-Doo: Mystery Incorporated] In the final episode after destroying the Evil Entity, why did this suddenly altered reality to where the Entity never existed?
gpt
I assume it's a matter of temporal mechanics. That creature must not exist entirely in a single time, so it being destroyed caused effects that were, from our perspective, before the cause, destroying it before it ever influenced the species of Earth despite the destruction happening well after. 

Mystery Inc are basically refugees from a destroyed timeline, in which talking animals exist, who have found themselves in a world where that never occurred.