Why did we leave Iraq but stay in Afghanistan?

I am a bit surprised that more people aren't familiar with this.  The news broke over a year ago.  NYT: US Identifies Vast Mineral Riches in Afghanistan

WASHINGTON — The United States has discovered nearly $1 trillion in untapped mineral deposits in Afghanistan, far beyond any previously known reserves and enough to fundamentally alter the Afghan economy and perhaps the Afghan war itself, according to senior American government officials.

The previously unknown deposits — including huge veins of iron, copper, cobalt, gold and critical industrial metals like lithium — are so big and include so many minerals that are essential to modern industry that Afghanistan could eventually be transformed into one of the most important mining centers in the world, the United States officials believe.

In addition to those minerals, there was also discovery of an enormous quantity of rare earth elements concentrated in a small area. Huge rare-earth material in Helmand: USGS  

The Khanashin carbonatites in southern Helmand Province have an estimated one million metric tonnes of rare earth material, according to a US Geological Survey (USGS) estimate...

Rare earth elements are important ingredients in high-strength magnets, metal alloys for batteries and light-weight structures and phosphors. These are essential components for many current and emerging alternative energy technologies, such as electric vehicles, photo-voltaic cells, energy-efficient lighting and wind power.

Products containing rare-earth elements also are used in a number of key defence applications More than 95 percent of global REE production now comes from China, which in 2010 exported approximately 30,000 metric tonnes of such products.

Mining offers a fast track to modernization for Afghanistan. The influx of capital investment for new mining operations and the cash flow the mines generate will bring economic growth and a functional infrastructure to the remote provinces.  No invading force has been able to maintain a long-term presence in Afghanistan before, but then none have done much to help the people of Afghanistan develop their economy, choosing instead to focus on maintaining military dominance.  

Two of the minerals in particular, lithium and the rare-earth elements have special significance for the future of the energy grid and the electrification of the automobile by enabling lightweight battery technology and motor efficiency gains that will in turn reduce oil consumption and carbon emissions.   As the mines increase output, the additional supply will lower market prices benefiting both consumers and manufacturers around the globe.  Mine baby mine.

It makes strategic sense for the US to maintain a meaningful presence in Afghanistan long enough to enable both the development of the transportation infrastructure and stabilization of the Afghanistan government needed to enable the new mining economy.  This is an important economic, political, and environmental mission for the USA all enabled by the brave men and women in the US Military and our coalition partners.