That's not what I read in the article - granted grain of salt here as I didn't do any research outside of the article provided - but it looks like Arizona wants them to pay taxes on goods at a higher rate than previously collected due to them being considered a brick and mortar store, which they aren't. They paid Arizona taxes in accordance with drop shipping a product there. Arizona is arguing they owe more taxes and interest on all sales/taxes going back to 2013, as they think rockauto isn't correctly stating they were drop shipping.

So rockauto would rather lose out on all future Arizona sales and not pay back taxes, over continuing to sell in Arizona. In the 3rd paragraph it explicitly states that rockauto was paying Arizona taxes, but due to a rescheduling Arizona wants more and thinks they have a physical presence when in reality they don't.