Because MM2 gates access to Demonic gorillas, a key piece of content in Kandarin which would otherwise be unavailable.
DS2 blocks access to Vorkath which does the same for Fremennik.
Dorg really isn't a significant piece of content and one that everyone could quite honestly not have access to and not bat an eyelid not to mention that everyone gets Misthalin for free so it's not like there's a choice being "not picking Misthalin because it doesn't have dorg".
Contrary to your other comment, we spent A LOT of time reviewing this, again and again, making changes and putting out our decisions infront of the community for more feedback, that's why the area interfaces were available ahead of time in the League so that we could pre-empt anything we may have missed, since afterall, this League covers an extremely large amount of content opening up the entire game world. We've have been fools to think we could've thought of everything ourselves