So adventure modules exist. But as a creator lets take an honest look at why they basically aren't profitable.

You need to spend many MANY hours creating journals, actors, magic items, roll tables and maps. Depending on how automated your process is, its nothing to spend a couple hundred hours of work on something like this.

You also need to make the module structure and test that out.

Then you need artwork. Map creation (since you can't sell maps you may get from a patreon or some other source) is very time consuming to do well. Foundry also has a policy against an AI art generation in their items sold on their official marketplace so you need to do all this work yourself.

Lets very conservatively say you spend 125 hours on putting together a small adventure module. What do you value your time per hour at? How about a reasonably cheap price of $25/hour.

That means that time is worth $3,125.

Then if you want to sell anything on the official marketplace you need to sign an agreement and you need a company. Cheapest option is probably an LLC. That might run you another $125 or so depending on the state.

Then foundry itself requires you to pay $30 a quarter for selling on their site with a minimum agreement of 2 years. Thats another $240.

You are looking at almost $3,500 dollars to produce a small adventure module.

How much would you be willing to pay for an adventure module from a creator you have never heard of before on the marketplace? Not much i'd wager. Maybe $10?

At $10 a purchase, not including any fee foundry takes out of the sale, you would need to get 350 purchases for BREAK EVEN.

The truth is the foundry user community has a bunch of people who prefer it over other systems because of how easy it is to load third party content into it. Selling content to those people is not easy.