One of the reasons WotC are currently focusing on their storylines is that D&D doesn't currently have a lot of marketable characters - there's Drizzt, and Strahd, and a few others, but not many. That doesn't give them a huge amount to hang future movies (novels, games, etc) on. So by creating their storylines they create recognisable characters that they can then sell. Eventually, they may hit on one that gains significant traction, and that will give them something to license out.
(Please note: "one of the reasons", not "the reason".
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This is a good point most people miss when looking at D&D the Brand.
Marvel can put Spider-man on a T shirt and sell it. They can make a movie about Thor, a TV show about Daredevil, and an action figure of Captain America and each will sell. You can lather-rinse-repeat with DC, Star Wars, Lord of the Rings, Game of Thrones, etc, etc. Each has some iconic characters, settings, villains, and stories that are the lingua-franca to those involved.
What does D&D have? Well, few recognizable heroes. Elminster, Raistlin, Drizzt, and maybe the Heroes of the Lance? None of them are really Iconic of D&D. D&D lacks a strong "stable" of heroes, that's usually because the Heroes of D&D are you and your elf, a hard concept to put on a T-shirt. So you go on to other portions. Settings? Well, D&D has an infinite number of them. Even if we just limit to published ones, you still end up with a lot of divergence. I suspect they will one day embrace the "worlds of D&D" concept, but right now, they are focusing on One World (Realms) to keep some cohesion. Villains? Well, that's a little longer list. Tiamat, Lolth, Strahd, Soth, King Snurre, Accerack, Lady Vol, The Anchromentals, Orcus, Asmodeus, all good villains. But a villain alone is never enough, and here is where you get Story. Shared Stories are the only thing D&D has to offer at the moment. People who have played recognize the Wand of Orcus, the Demon Head in the Tomb of Horrors, The sphinx riddle from White Plume Mountain, and yelling Bree-Yark in the Caves of Chaos.
Thus, the team decided the best way forward in creating a shared vision is to give us all iconic stories to tell. You and your elf go up against Tiamat and the Cult of the Dragons, it becomes a shared experience across players like the 1e modules of Olde Tyme did. No two DMs are going to do it the same way, but the players will (hopefully) be able to share the time THEIR elf stopped Tiamat.
I admit its not much for the obsessive homebrewer, but I've found (myself included) these guys rarely need much support. I do hope though we get some non-AP supplements.