There just aren't that many available water sources to draw large amounts of water from, and El Paso is going to be pretty much at the bottom of the list when it comes to irrigation supply. The Colorado is already oversubscribed, and tapping new water sources creates political backlash from locals who don't want to see their water going to other counties or states. Finally, pipelines are expensive beasts in a time when the federal government isn't interested in eating the costs and state governments can't easily wait for counties to pay back out of water sales.

Water is a bit odd in that it's ridiculously cheap even where it's scarce, so the financial incentive to build massive water-diversion projects isn't all that great absent a specific political or governmental imperative. It's also dubious that it's worth diverting water to places that are naturally scarce (or where wasteful policies have drawn down aquifers and other groundwater sources). Pushing the carrying capacity of a region well beyond its natural levels is a fraught enterprise, especially if the regions haven't shown themselves to be particularly good at managing their current water stocks.

Personally, I'm betting that in 20 years the Great Lakes rust belt is going to be enjoying a hell of a resurgence.