Of course, rhe economical argument requires you to subscribe to the idea that the fetishes and foci could be anything more than a ridiculously small niche market.
Hmmm.
A common percentage put magically active individuals -
usefully active individuals - at 1:1000. With 7 billion souls, that's a market of seven million - or even just seven hundred thousand, if it's 1:10,000. Yes, across the planet, but if you have exclusive access to a gold field, the seven million (or 700,000) people who can afford pricey gold rings are
still gonna mean you can make a good deal of money off that 'ridiculously small niche market'. A mage who puts fetishes to great use is spending between ¥50 and ¥500 per fetish; think of those in terms of 'dollar', if that helps you wrap your head around it better. $50 to $500 to 'do my job better' - a combat knife, or a pistol. If he's burning them up, hell, he's a money tree for you.
And remember, fetishes are
not the only use of reagents - just the
least expensive ones. Conjure and bind a F6 spirit? Build a
focus?? Cripes,
military combat vehicles can be less expensive than a single powerful enchanted focus. God help you if you
stack the damn thing. (And yes, like many things in SR5, magical gear is significantly ... altered, let us say.)
All this means that though the
number of individuals may be specific and limited, the combination of market size, individual item expense, and unique demand (because you can be sure corps stockpile reagents &c. just as readily as they do bullets and grenades) means that trying to acquire exclusive control of a reagent-rich area is just as economically sound as trying to acquire control over any
other resource zone.
Here, let's do some math. Presume those one-in-a-thousand - no, let's pare it down further, one reagent-using individual in ten thousand. Say every one of those 700,000 people uses
only an average of ¥250 in reagents per month. That's between 12 and 13 uses per month, averaged out across the board. Going by that base amount, for each one of those 700,000 people, that's a market of ¥175,000,000 per month - or ¥2.1
billion per year. Increase your mystic quantity to one in a thousand, and that's ¥21 billion a year. Sure, you'll probably sell more in Choco-Melon Super-Squishees, but that's an
awfully low 'price point' we're starting out with - and after all, they
do still sell Choco-Melon Super-Squishees at the Stuffer Shack ...