Barbie can have a message attached to it because of its history as a feminist icon and a controversial toy. They can actually tell a meaningful story based on it.
I can’t think of a single exciting new idea that Hot Wheels, or really any other toy for that matter, could have. What could a hot wheels movie end up being other than a Fast and Furious knockoff?
But I was wrong about the Lego Movie, so it’s not unlikely for these studios to come up with something ridiculous and execute it well.