2 reasons: first, we don't really use that state-of-the-art stuff against them. Most of these conflicts are being executed with comparatively boring, conventional means. The railgun, however, are a marked improvement over current naval-based artillery, and allow us to strike much further inland with them. Its a lot faster, cheaper, and safer to fire a cannon than to send a plane with a bomb in certain situations. The cutting-edge toys are used as deterrence mechanisms for other more sophisticated countries, which we have healthy diplomatic channels to communicate over. My comment above explains why merely having them is necessary and sufficient in most cases, especially since other powers are developing similar tech.

Second, we are much more squeamish about losing American lives than we ever have been before. Any administration that chooses to throw bodies at the problem like we did in both World Wars will be quickly replaced. I can't defend every project (especially not the F-35), but by and large this tech is designed to maximize effect with minimal risk to American lives.

Because those rice farmers and goat herders are armed with man-portable anti-aircraft missiles, explosives mines, assault weapons, and in a future conflict, likely lasers and railguns too.

...that we sold them when they were fighting for us.

If they were ill-equipped in Vietnam, ill-equipped in Iraq and Afghanistan, then why would potential combatants suddenly come into possession of weapon systems more expensive than their nation's GDP? World powers don't just hand out state of the art weapon systems all willy nilly, lest they end up falling to the enemy.

They were equipped by the Chinese during Vietnam, and they were very well equipped by the USA in Afghanistan (the original Russian invasion). Everything the Iraq army has ended up in the hands of various resistance and terrorist groups (including ISIS).

The article is about highly advanced anti-aircraft and anti-ship weapons. They don't even have armored infantry, let alone those.

It's a stretch to call them "ill-equipped" in Vietnam and Afghanistan, considering that the insurgents won both campaigns (with generous military assistance from the opposing superpower). No, they didn't have armored infantry - but they had surface-to-air missiles, anti-personnel mines, anti-tank missiles, and automatic submachine guns, all provided by the opposing superpower. The U.S. lost many aircraft against the North Vietnamese, and the Soviets lost many tanks and helicopters against the mujahideen in Afghanistan.

steve19 also makes the very good point that these weapons did fall into the hands of the enemy: most of the Taliban were trained by the CIA, and the weapons our forces faced in Afghanistan were largely ones we had sold to the mujahideen in the 80s. Now the weapons left behind in Iraq are largely in the hands of ISIS.

The point of this article is that the U.S. is likely to face similar asymmetric threats in any future war, where the opposition doesn't have the same weapons as us but they do have weapons that are very effective at countering us.

Because those things aren't purchased for national defense. Their sole purpose is to sustain the MIC as part of a self-reinforcing money grab just as General Eisenhower warned.