Well now, we're getting into the micromanaging element. Yes, as a DM I can rule yes or no on any given item, but realistically, how often does a DM claim you (assuming you have coin and are some area with reasonable trade*) you can't buy plate armor? Heavy Crossbows? A boat (near a body of water)? 200 feet of rope? All of these things are just as susceptible to market flux, but few DMs I've ever seen care about supply and demand of goods.
TBH, but for the "Monty Haul" years, that kind of treatment of scarcity has been the norm over my gaming career.
As I mentioned above, when in RttToEE, My PC was unable to have a masterwork dire pick made. Rarer than plate armor, yes, but not exceedingly rare.
The same guy GMing RIFTS had the party constantly scrounging for ammo, and we really didn't have much in the way of transportation.
In HERO, a different GM (in a different city & group) made it virtually impossible for the party to hire agents to take on the agents of evil organizations, so we were almost always outnumbered when we encountered groups like Viper (that game's version of Cobra).
Again, the GAME ITSELF doesn't take these things into account.
...because it is left to the DM to decide whether he'd like to do so.
Personally, I don't expect a game to handle every eventuality or possibility. In the 100+ systems I've owned! I've yet to see one that does. In fact, I can't think of one offhand that handled things like rules for natural disasters (except maybe plagues), strikes, embargoes, derivative effects of war, oligarchs playing chicken with the economy, and so forth. Their rules are almost solely focused on actions at the PC level. All that other stuff is glossed over if addressed at all.
And yet, they can make the play environment richer and more challenging. They can even make for great plot hooks for adventures or story arcs.