So take these cheapie eastern night vision division devices: Good for a range of 150-200 meters depending on context, around $700 a pop. Both goggles/binoculars and rifle scopes for different contexts.
To equip the line personnel (defined here as those in the actual fighting regiments/brigades) of one small division in the absolute most oversimplified fashion would be around $7-10 million, depending on the exact size. Getting around 5,000 sets, but then there comes the hard part: Maintaining 5,000 sets, keeping track of 5,000 sets, making sure that those 5,000 sets aren’t lost (via honest or dishonest means…), and so on.
Now apply this to almost any even slightly expensive piece of military equipment and you can see why, for instance, Egypt still issues its draftees equipment left over from the Yom Kippur War. That’s an extreme example, but you can see how even the individually “cheap” stuff can be expensive, particularly for less funded armies. And you can see both the political and military advantage of reserving such a thing for “elite” units if one has no choice but to only acquire a limited number of said items.
And you need a lot of stuff, to the point where it’s almost an “I, Pencil” situation. Boots, uniforms, load bearing equipment, helmets, packs, shelters, it all adds up. The bottlenecks can appear where you wouldn’t think they would. For instance, many people know of WWII Germany’s fuel shortages, and historians know of their special alloy shortages, but what a lot of either don’t know is of their cotton shortage resulting in less effective leather load bearing equipment.