I’m a bit late on this but…
Personally, I think the problem is the fact that the Sonic movie is live-action, ergo, it will be bad. Well, the issue isn’t entirely reliant on the live-action-ness of it, as it’s probably the plot that will be the biggest one.
The Pikachu movie looks good, and despite the shift to a live-action, realistic style, it looks enjoyable. The thing is, it still works. The show/game property are all about modern human people who train and befriend the various animals that roam the land. That’s not entirely the plot of the film, but the world-building is still present.
Sonic (to my knowledge, I haven’t played any) is about a bipedal fast Hedgehog who lives in a fictional world very unlike our own. He saves the animals from the forest from being kidnapped from a spherical man bent on turning them into robots.
The concept of a live-action Sonic movie makes no sense (to me), and I can’t see any way they can adapt that to fit the locale of the film.