If you're conversant with negative Commerce Clause doctrine — AKA the "dormant" Commerce Clause — then you know why the Supreme Court split the way it did.

The case that came out this morning is National Pork Producers Council v. Ross.

Gorsuch announces the judgment. Much of what he says is joined by the conservatives Thomas and Barrett and by the liberals Sotomayor and Kagan, and some of what he says is joined only by Thomas and Barrett. The Chief Justice concurred in part and dissented in part, and he was joined in that dissent by the conservatives Alito and Kavanaugh and also by the liberal Jackson. There are some additional opinions by Sotomayor, Barrett, and Kavanaugh.

The Commerce Clause — which empowers Congress — has been interpreted to bar the states from discriminating against interstate commerce and, more controversially, from putting too much of a burden on interstate commerce. The California law in question in the case forbids the sale, in California, of meat from pigs that have been raised, anywhere, in a manner California deems cruel. 

The split among the conservatives seems to be between those who favor judicial restraint and federalism and those who want more freedom from regulation.