Question: why are mogu in zandalar?
Answer: Thousands of years ago the Mogu entered a pact with the Zandalari, because they were the strongest empires on Azeroth. To make a long story short, the Thunder King was blown up by the Tol'vir using the Halls of Origination in Uldum, and the Zandalari waged war on Pandaria, where they were defeated and driven back.