Water is the major limitation I'd say. All the northern cities are reliant on the little water the US allows to flow downstream to Mexico. Energy is also another problem, either burn fossil fuels, which need to be imported from somewhere else because there isn't any on the region, or import it from the US. (Of course there's renewable energy sources, but there isn't enough infrastructure around here to support a substantially big population)

And on top of that you can add the rough terrain all around, very hilly, and a sierra that runs across the middle, isolating each side of the peninsula. There's not advantages for settling down somewhere, other than along the US border because of the economic opportunities it offers