1) Because she can do it. After Vaes Dothrak she will have the largest army in the world. 2) Because geographically she needs to do it. If she wants to head West, she needs to pass through some of these cities. In particular Volantis is unavoidable. Armies need food and water and plunder. Ships needs to be resupplied and repaired. And she needs to finish the slave market once for all, otherwise she will leave behind a multitude of Astapors. 3) Because there are hanging plots that need