Reputation is big in this. Paizo had a good rep, and still does, when it comes to APs and adventures. WotC starts with a bad one, even before 5e was released. They are putting all their eggs in a pierced basket.
It's worth noting that Wizards is not actually writing these adventures, and that anyone with enough investment in the history of the game to know about Wizards' past failings is also going to know that. I apologize if that sounds dismissive; it's not my intention to suggest you don't know what you're talking about. I'm just trying to make a point. I'm sure we both know and respect some of the names behind Sasquatch just like we both know and respect some of the names behind Kobold Press. I feel like Wizards has recognized their shortcomings and made a good faith effort to overcome them.
Also, WotC is just recycling adventures. We saw the theme of elemental evil/Tharizdun a couple of times before. Heck, Tharizdun was not too long a go at the center of the Abyssal Plague, a cross-setting set of adventures and novels during 4e's reign that didn't generate much enthousiasm. Now they just set the same adventures in the Realms and do not even bother with previous cannon. The issue goes beyond marketing and having some crunch a bit of fluff in their AP.
I really don't want to be in the position of defending Wizards on this because I do feel that they are hiding behind FR and it pains me greatly to see lore from other established settings sucked into FR without even the barest attempt at justification beyond, "The forces of Elemental Evil tried to invade Oerth and failed, so now they're giving Toril a try." That's not an acknowledgement of the D&D multiverse; that's what we call not having the strength of your convictions.
I have every confidence that we will eventually see APs from other established D&D settings, but in the interim it's clear that we're going to see a lot of core fluff -- material that, for instance, would have found its way into Nerath in 4th Edition -- absorbed by the ravening gelatinous cube that is WotC's Forgotten Realms. And of course the real tragedy there is that once a product is produced you're obviously not going to see that same product produced for another setting. So the move is permanent, at least until D&D6. Disappointing.
With that little rant complete...
What Wizards is doing is not recycling adventures. They are recycling /themes/, which is exactly what you do when you have a strong brand like D&D. You wouldn't find it unusual for a future iteration of the Transformers franchise to have a story involving the All-Spark or energon, and you wouldn't find it unusual for an X-Files reboot to involve black oil or feature a mysterious power player who chain smokes cigarettes. I may take issue with how they are doing it, but what they are doing makes good sense.
Saying that this is recycling adventures is like saying every adventure to feature an orc horde -- or a lost temple, or underdark dungeoneering -- is the same adventure.