Faster and more productive Railways: Auckland to Tauranga via Hamilton

Auckland,Hamilton And Tauranga are 3 of the Main cities of New Zealand And they are all under 200kms Away from the Auckland CBD Why not make a faster and more productive railway from Auckland to Hamilton? The Auckland council and Kiwi Rail have Proposed a double track railway network between Hamilton and Tauranga. 

Auckland is Meant to grow by 2 million more people by 2030. which that will make Auckland have 3.4 million people by 2030. This is that type of connection Auckland is going to need to Connect the World  to Auckland.

The Auckland Tauranga railway is  already very well constructed because a lot of cargo goes from Auckland to Tauranga But what I think is the Main focus Should be Auckland to Hamilton Because lots of people from Hamilton Come up to Auckland To do a lot of  Business. But The question I am wondering mostly is Why they did not do this earlier?