Jayzus! If I never heard this "truism" again in my life, I'd be happier for it. Ever since Ryan Dancey offered this nugget of wisdom back in 2000, it's been automatically repeated over and over. It was certainly true in regard to TSR's business model, but times have changed. Even Dancey and his immediate successors released (or licensed out) a ton of different settings during the post-TSR 3E era: Eberron, Diablo II, Kingdoms of Kalamar, Warcraft (D&D branded), Wheel of Time, Dragonlance, Blackmoor, Gamma World, and probably others I've forgot. And Hasbro likewise released some settings for 4E: FR (which, if you'll remember, wasn't the core setting in 4E), Eberron, and Dark Sun. All of this happened after that "truism" was well known. Presumably these settings weren't total losses from a business perspective
Even recently, WotC has found a way to make Ravenloft profitable: released as a one-shot, iconic campaign sampler. Even Adventurer's League visited Ravenloft through a world-hopping adventure which leaves from Toril and then comes back to Toril at the end. The same could be done for all the D&D worlds. And 5E has already gone so far as to actually list the names of all the classic worlds in the PHB and DMG, and to give conversion notes for several of the worlds in some of the 5E adventures.
And...one big difference between Paizo and WotC is that WotC does hold a wealth of different settings in its stable, which still possess the power of nostalgia. This is an untapped asset. That's why even WotC's rep recently posted: "people want settings!"
Just because you disagree and want something hard enough doesn't make it not true.
Multiple settings were not good for TSR and divided the market. Greyhawk fans only bought Greyhawk adventures and sourcebooks and not FR ones. The fans weren't "D&D fans" but "Dragonlance fans" and "Ravenloft fans".
The hard fact is that you only ever need one or two campaign settings. You can play dozens of campaigns in each campaign setting. By their very nature these products suffer diminishing returns. The first might sell well, but by the third or fourth they're barely going to sell enough copies to remotely be of interest to WotC. Because people will already own a setting.
You don't even have to look far to see that. In 4e, they dropped the campaign-a-year plan after just three years. People weren't buying the settings just to own them, but were waiting for the settings they did care about. By the third year of 4e, they were back into the Forgotten Realms.
Campaign setting books are also largely edition neutral. If they were such great sellers, why didn't they keep releasing them between the editions? Easy money between 4e and 5e...
Settings are always going to be a niche product compared to accessories, monsters books, etc. The majority of D&D players (54%) make their own world. And many of the rest default to the Realms (37%), likely because the adventures are set there and not because they have any affection for the Realms. Right now, only 5% of D&D players make use of older edition settings.
Most players simply are not going to care. And if you bring in a brand new setting, even fewer are going to care. Why would they? There's no shortage of campaign settings already on the market and it's not like having it branded "D&D" will suddenly and magically open people's wallets.
You can get around this by having one of the storyline adventures set in a different setting. Like Ravenloft. But that adventure didn't *really* update the setting: it updated the classic adventure and stole some names and locations from the campaign setting and used them in largely unfamiliar ways. And, really, that sold because of the adventure and not the setting. I doubt many people cared about the setting.
I moderate a Ravenloft fan community, and I can tell you that we very much did
not see a sudden surge in Ravenloft fans following the release of
Curse of Strahd.
Which gets back to the "why??". Why release this campaign setting no one has read outside of WotC. There are a couple reasons.
* First is that they own it. Which isn't a particularly big deal. As noted, they own like fifteen settings, and are only doing stuff with two. And that's not counting the settings people worked on for TSR that never made it past the planning stages. (There are a few.) What's the benefit it making it sixteen?
* Second, it's a new setting that isn't like the ones released by TSR. Okay, neat. But the same could be said about the
Tal'Dorei Campaign Setting or
Midgard. Why not back them instead?
* The third reason is that it's the work of Rich Burlew. Which is neat, but by the time it's expanded into a full book... it will be 33% the work of Burlew (and much of that being ideas recycled elsewhere) and 66% other authors.
And it's not like most D&D players really know who Rich Burlew is...
That last point is the BIG catch.
I love OotS as much as the next guy, but it's not really a growing comic. It's hard to get into, takes a while to get good, and the first strip is based on a fifteen-year-old edition change. Often times, I barely get the mechanics jokes anymore because my 3.5e muscles have gotten so rusty. And those aspects aren't going to get any more relevant in the ten years it's going to take to finish the story. Especially at the rate of one strip a week: the current book has been ongoing for just past four years.
Remember the amazing OotS Kickstarter? That came out the same years as the 5e playtest. And the following book came out a couple months after 4e launched. And that's well, well after the massive wave of 5e fans pretty much doubled the audience...
I'm not sure why they should release some random new fantasy setting. It feels masturbatory. Content for the sake of content.