Agreed, and I'm not arguing that. Wizards definitely benefitted from the OGL. I'm arguing that a business plan that involves your customers leaving and eventually coming back with no direct balance sheet number is not a scenario a board of directors would see as a benefit.
But the rationale for OGL support in the new iteration has not changed from when they decided to do it for 5e. For good or for ill, D&D was released until the world in 2000. When they tried to take it back with 4e, they inadvertently created their biggest competitor. I expect the pitch during 5e went, "Look, there's already all these 3rd parties making things for 3.5, feeding the size of that market. If we keep 5e restricted, they're going to keep doing that. But if we open up 5e, all those 3rd parties start making stuff for
us, feeding the size of the 5e market. Then, by maintaining the DM's Guild, we even get a bite of that apple."
Now 5e is even more popular than 3.5 was. And that board of directors has seen what happens when you try to go back like they did with 4e: a lot of people come with you, but a
lot stay with the old edition.
Historically, RPGs are hard to maintain as a business. Even the biggest, most popular one of them all sells a lot of core books, sees diminishing returns on non-core book products, and then starts to see reduced sales of the core books as the market reaches saturation. Gygax couldn't make it work. Lorraine Williams couldn't make it work. Until 2014, WotC couldn't make it work. Now, even accounting for something of a fad effect through Critical Role/Stranger Things, they seem to have hit upon something of a successful model: release the core books as your main drivers of revenue, release a free version of Basic Rules to grease the on-ramp, release two major adventures a year (with accompanying storylines you can seed through other products), and supplement that every couple years with a sourcebook of new options. The whole point of this is to stimulate revenue while keeping production costs manageable. (This lesson learned from the TSR '90s.)
And the OGL/DM's Guild only aids that plan by taking off the burden of trying to service the whole of a SUPER DIVERSE market. The people not satisfied with the streamlined product line put out by WotC are still incentivized to buy the core (and some other) books, because their needs are met by OGL/DM's Guild creators.
The line on the balance sheet that the board of directors really care about, as far as products go, is profit. D&D currently has a very good case that the OGL adds to its profit line, should the board of directors micromanage enough to care about the OGL.