So what's really going on here?
Missouri Attorney General Koster said in that same press release that "[i]f California legislators are permitted to mandate the size of chicken coops on Missouri farms they may just as easily demand that Missouri soybeans be harvested by hand or that Missouri corn be transported by solar-powered trucks."
That's a pretty emotional argument, especially coming from the state's top lawyer. He apparently made those sorts of (grandstanding) comments to the Missouri Farm Bureau before filing as well. That might explain (the sheer arrogance of) his legal demand (to a court that sits in California no less) that it restore a competitive advantage to his state at the expense of that court's home state.
But perhaps there's a bigger observation to be made here. Regardless of viewpoint, most people would agree that environmental, consumer, and more recently, animal-friendly laws are becoming more the norm than the exception. As the tides shift, those who oppose laws that don't put people - if not specifically themselves - first are increasingly the ones resorting to impassioned, and even vitriolic, pleas. Anyone else remember the protests when England banned foxhunting about a decade ago? British lawmakers had to suspend parliament in order to physically remove pro-hunting protesters who had barged in and disrupted the debate.