If you look at countries across the world their economy is dependent on their largest cities in terms of revenue generation, employment and innovation.
I agree more money needs to be spent on health and education. But if you divert all your money to education then it would take perhaps 25 years before you start to reap any benefits and so with health. Infrastructure spending benefits immediately, enhances trade, creates employment and should result in higher revenue generation which can then be spent on education and health. Infrastructure spending also makes the lives of people better.It is something that is visible that people can see and will vote for.