For a start, that’s the bit that is roughly the same area as the Lahsa eyalet, not the interior. Riyadh province, which is in the middle bit, has eight and a half million people. Add in al-Qassim province which is also in that area and you have ten million.

But also, just generally… five million people is a lot of people. It’s not like it’s even a particular outlier in terms of density. The eastern province is more densely populated than Canada.