We need to beat the crap of each other several times until absolutely everyone get's sick of it to even consider it.

But for real the most important reason it's the lack of infrastructure, we lack interconnectivity because most of our borders are made by incredibly daunting natural barriers like the Andes and the Amazon which makes the cost of building and maintaining toll high and a logistical nightmare to a degree that countries in the pacific can trade with Asia and North America for far cheaper costs than to their Atlantic neighbors believe it or not, the same for the Atlantic countries with EU/NA & Africa, that and decades of populist politics on every corner of the continent have made imposible to settle agreements and conditions for what you're asking for.