It would be rather naive of them to think like this. Share holders don't want to wait 15 years to see a return on their profits if you want to look at it from a business point of view.
The shareholders of WOTC know the company's profits will be fine. They sell Magic, which makes WAY more money than D&D. Their D&D plans don't even show up. Plus, I don't even think WOTC is publicly traded at all. It's owned by Hasbro who is publicly traded. Their D&D plans will not affect the stock in any way at all.
Also, Wizards don't know better than we do as to what we want, 4th edition is evidence of that.
Except for all the people who loved 4e, the large number of books sold, and the large number of people I can't convince to play 5e at our local stores because (and I quote) "4e was the best edition of D&D and I can't believe WOTC is trying to sell us this stupid 5e", you'd likely be right. Our local store went from 16 people playing D&D Encounters to 6. The other 10 explicitly stated they were quitting because it wasn't 4e anymore.
They were right that 4e would appeal to a lot of people that 3e didn't appeal to. Our group switched. A LOT of people liked it better. Many of them were from within the Organized Play community. I was a volunteer for WOTC during Living Greyhawk. A large number of people were super happy to see things we'd hope would be fixed for years finally being fixed in 4e. WOTC listened to us because we were the people they had the most direct contact with. We were the people filling their game rooms at GenCon and Origins where WOTC employees actually had the time to talk to customers directly.
Our issues were about game balance and consistency. We wanted every table to be DMed exactly the same and we wanted everyone who showed up at the table to be equal in power and in agency in the game. We voiced those concerns and got a game with greater rules, greater consistency and greater balance.
The fact that there is an extremely vocal community of people who absolutely hated it did not mean that WOTC wasn't listening to their customers when they designed 4e. They just happened to listen to a group of their customers who had different priorities than another section of their customers.
If they are dried up with ideas after only a few products then maybe the current team shouldn't have been hired in the first place. Usually companies want a long term plan in place that will generate profit. Of something is planning on dying in 5 years, they are not going to stretch it out to 10. They would just be satisfied with picking up those profits as quickly as possible.
I believe there are only so many GOOD ideas before you start getting to "alright" ideas. The books near the end of 3e were starting to be stale and kind of boring. I truly think 3e managed to exhaust all the good ideas. I think the number of books released from the beginning of the cycle to the end of the cycle was about the limit before they HAD to release a new edition or end up released "Complete Sock Drawer" as a book.
So, assuming this is true, then you don't want to release all of the books at once because then you have nothing left to sell and all of your jobs go away. D&D is a niche brand. Niche brands rely on good will to prosper. Fans will continue to buy books year after year because they *LIKE* D&D and they have good feelings towards it. If the general opinion of their books is that the last one was stupid and was filled with bad ideas that weren't playtested well enough then no one will buy their next book.
For a company like WOTC who already makes 95% of their money off of a different product, they would rather have a small team dedicated to D&D who releases 2 or 3 products a year that barely make enough money to keep the department open as a labor of love for something they loved as kids than to exhaust all of their good will wringing all the money they can out of it and letting it die.
They have the luxury of not caring so much about how much profit they make on D&D. If D&D breaks even and they can make a movie deal and a video game deal and use those contracts as profits...then perfect. If breaking even on the game means that 10 years from now people are still saying "I loved D&D! It's great. There's an expansion coming out for it in 6 months! And Sword Coast Legends 3 is coming out this year! That'll be awesome. Also, I just bought the new Forgotten Realms novel and the D&D movie 2 is being released in December!" then they are happy. If people are saying 5 years from now "There's another edition of D&D coming out? Yeah, I'm tired of this crap. I'm getting off....WOTC ruined D&D and they aren't getting any more of MY money. Especially after I bought a book a month for 5 years now!" then they will have to shelf D&D and never release anything again. That isn't good for anyone.