If what WotC said in the recent article about how they have 12-15 million players in NA is true, then they are way more massive then what 3rd party success would lead one too believe. On a lot of forums outside of EnWorld (and sometimes, even on EnWorld), 3rd party material is always treated as a last resort and very rarely pulled from. After all, when you have a playerbase of 12-15 million, those 100-500 backers on Kickstarter suddenly don't seem like so many. Even if each backer represents a full party of 5 eagers players, that's still less than 1% of the D&D market.
Thoughts?
Obviously there are a lot of reasons. A few possibilities.
The amount of time people have to play vs. how many things are available.
Distribution - kickstarter/internet is one thing, being in every game shop and other outlets another.
3rd party products often cater to a specific play-style or approach. They are frequently more of a niche product.
D&D and 5e in particular are very friendly to homebrew content, much like OD&D and AD&D were.
A 3rd party product might not be approved by the DM, the players, or both.
The quality of WotC is a known quantity. This includes things like game balance, type of story, content of story (and content that won't be in their products), etc.
Expansion material has always had a much lower usage rate. Not just sales of adventures, but publications like Dragon and Dungeon magazine when they were both print magazines. The core books sell many times more copies than the WotC adventure paths. 3rd party sales will almost never be more than a percentage of WotC sales. So a WotC adventure path might sell x copies, and a 3rd party AP would sell a percentage of what they'd sell.
Note that to this last point, Pathfinder is an outlier. Although the reality is, there wasn't a point where you could compare (if you could get numbers), a WotC 3.5e adventure released in the same month of a Pathfinder adventure. It was more a question of whether they liked WotC older or newer game system better.
The WotC sales also reflect a fair amount of turnover. That is, me playing for 35+ years is less common than somebody that plays for 4 years at college and then moves on. New players need the core books, and every year there are more adventures available. So new players have more material to "catch up" on before considering 3rd party materials.
The business model is different. 3rd party releases don't need to sell millions of copies to be viable. WotC has much higher overhead, and must remain a valuable asset to an even larger company. So 3rd party releases don't have to spend as much on marketing, distribution, etc. As long as they are meeting their sales goals, they are a success, and can cater to a niche market if they want to. Want to make a campaign setting of entirely reptilian/dinosaurian races? Go for it, it only has to appeal to a small group.
I love the stuff we do in our campaign, and I'm happy to share, and might even publish some of it eventually. But I'm not attempting to cater to a mass market. In most cases, the appeal of the material produced really is much narrower than that of the WotC materials.
Now I can also envision a scenario where 3rd party stuff sells nearly as well as a WotC release. By licensing their settings to the original setting creators (who can also bring in some of the setting's most popular contributors). For example, instead of WotC producing an updated Forgotten Realms campaign setting, have Ed Greenwood and friends do it instead - and make it official. That is, WotC will only publish materials that work with the Greenwood published materials, and vice versa. A solid licensing agreement for Dark Sun, Eberron, Ravenloft, Forgotten Realms, etc. would allow for a huge increase in 3rd party materials that would probably sell in large quantities.
This approach has already been taken by Sophisticated Games/Cubicle 7 an
Adventures in Middle Earth. Note that it's not really seen as D&D supplements, but it's own game. Some settings could be produced in a similar manner, with heavily reworked rules, and others could simply be a supplement to the D&D rules.
