Well said! Something to add here is that one business model used in the video game industry is to use expansions/DLCs to sell more of the original game.If it were simply delayed profits, they wouldn't. But a slower release may cause each product to sell better over time, increasing the return on investment. WotC might make more money through diverse investment in other games rather than trying to maximize the profits of the D&D product line.
There is also the possibility of perennial items beyond the core books. That's common with expansions to games like Catan or Dominion. Once a few are out there, they continue to sell without any development costs.
But I believe there is a limit. It would be harder to convince people to buy Catan: Cities and Knights if there were 20 expansions. But there are really only three. Not only is it less intimidating, but it also encourages people to collect the whole set.
This model doesn't work for all RPG content, but I do think it can work very well for rules. Possibly settings as well.
I know that for instance Payday 2 has had medium-large DLCs every 3-4 months. They generate a lot of publicity and actually make the original game sell a lot better. They have been doing it for 18 months now, and they still get the original game on the top 10 best seller list on steam. The game is heavily rebated, but the list is based on revenue so it actually sells really well.
Another similarity to Payday 2 is that WotC has been creating free content like the mass combat rules. This generates a lot of good publicity and is another way of increasing the sales of the complete 5e package.
I think WotC are doing the right thing to grow 5e for the long term, even if it means getting less sales to start with. I do wonder how a license would fit into this. I think that a license that would allow for third parties to make adventures would only help out, but it gets hard not to at the same time let someone do a Pathfinder and more or less copy all your hard work and use your brand as a marketing tool. (Paizo did an awesome job of it, building on their magazine knowledge, but changing it up, creating adventure paths instead).