Paizo's insane publishing schedule is possible because:
1 - They have a vastly larger number of employees than WotC's D&D division, though they pay most of them less . Cranking out that much material takes real and direct supervised labor (yes Paizo uses lots of freelancers, too); and,
2- Above all, direct sales via subscription.
Note that Paizo's product schedule, as large is it is now, was far larger in the 2013-2017 era when PF1 was the 500lb gorilla.
Yes, there are thousands of people who buy all of Paizo's product releases every month. Pawns excepted, I would be one of them. Numbers have not been officially released, but my guess (and that all it is - a guess) is that PF subscriber base is somewhere in the order of 8,000-20,000 regular subscription customers; a number which has risen and fallen over time. Whatever the case, that sort of predictable, bankable direct sales (with immediate cashflow) is core to Paizo's business model. Without it? That production schedule and employee base is not sustainable. With it? It mostly is. Mostly. Essentially, Paizo prints on terms in China, and on ship, their direct sales pay for the cost of the product - and then some. How much "and then some" is the devil in the details.
Still , core rulebooks, which can be printed in the hundreds of thousands of copies over the course of a game's life is where the real money is in RPG publishing, so WotC focuses on those sales via retailers. Those same FLGS retailers are the ones who generate the real money selling hobby games: which is to say, selling Magic:TG for WotC. [All RPGs taken together are modest compared to MAGIC:TG. It also explains why WotC has been reticent to sell directly. WotC depends on those retailer relationships.]
The direct sales model allowed Paizo to dominate the RPG business from 2010-2016. But when 5e started to gain some real legs in the marketplace, by early 2017, Paizo's retail sales via FLGS had dropped significantly.
Players like direct sales and the free PDFs a subscription provides. FLGS store owners? Not so much.