It is not "just focus on the North", it is give some focus to the North because the South has already had lots of focus and will continue to do so.
Strangely, this conversation reminds me of the "black lives matter" rational.
Either way, the North has been disproportionately impacted by lack of funding over many decades. It is a clear (ish) dividing line. But no dividing line is perfect.
Below is an older map (ore economic crash!) showing gross disposable income, which is one way to analyse the disparities. I'm sure you can find more up to date data if needed.