I suggest you read this to get some actual understanding of the situation.
https://eu.finalfantasyxiv.com/lodes...34483dabdcc490
Getting new servers is not all that easy right now - and obviously they can't buy just any old hardware, it has to be something with the right specifications whatever they are. And I think you seriously underestimate what they cost.
Oh, and just adding new servers to a data centre can't be done beyond a certain point, because all the worlds in a given datacentre share instance servers which handle all the instanced group content. They can only handle so many players at a time.