Was this technology not available at the time?
It was but for soldiers on the ground this usually translated to Night Vision Devices.
Pure infrared was more normally used by aerial forces for missile guidance and aircraft detection.
Why didn't "Dutch" and the commandos didn't bring thermal imaging devices like goggles or sensitive listening devices with them on the mission?
Obviously we'll ignore non-plot reasons but the simplest reason would be...
They didn't know they would need it.
Recall, as far as Dutch and his team are concerned this was supposed to be a simple rescue mission, in and out with little or no trouble in a short space of time.
Simple setup. One-day operation. We pick up their trail at the chopper, grab those hostages, and bounce back.
They might be expecting poorly armed guerrillas but not an alien hunting people down.
Also, I don't think the Predator was using an infra-red device, this is their normal vision.
Their vision operates mainly in the infrared portion of the electromagnetic spectrum; they can easily detect heat differentials in their surroundings but are unable to easily distinguish among objects of the same relative temperature