Reading it, I can see why.
Thomas believes that video games, by their "interactive" nature, are not protected speech, and doesn't agree with the idea that free speech automatically applies to new technologies.
Thomas is an jerk, but we knew that.
Breyer, on the other hand, makes the argument that games are protected by free speech, but that California's law doesn't prohibit the consumption of material to minors, only the sale of the material to minors. Viewed from that perspective, it places violent video games in the same category as Playboy magazine. Breyer doesn't make the argument that California has proven that games are harmful, he just makes the argument that it's not unconstitutional to restrict the commerce of goods from minors, and that the rules were not ambiguous or vague. Nor did it restrict consumption of speech - only the *sale* of it to a specific group.
While I happen to agree with the court majority opinion, I can see Breyer's point.