> The catch is that while the AV1 developers offer their patents (assuming they have any) on a royalty-free basis, in return they require users of AV1 to agree to license their own patents royalty-free back to them.

Such a huge catch that the companies that offer you a royalty-free license, only do so on the condition that you're not gonna turn around and abuse your own patents against them!

How exactly is that a bad thing?

How is it different from the (unwritten) social contracts of all humans and even of animals? How is it different from the primal instincts?