This actually is because of Walmart's business practices, and has likely very little to do with WoTC. Walmart is such a market force that they do and will dictate to other companies what they will sell the products for. And unless the product makers want to sell at somewhere else, at higher prices, they will abide with Walmart's pricing, or literally lose out on profits, meager as they are.
And the PDF purge was the last friggin straw.. I was stuck on duty and on deployment during the suitable length of time (48 hours) and was unable to recover my purchases. And their attitude on their forums.. blanket bans for questions.. (not trolling.. simple questions) was mostly the last straw.
The bold sounds more like the early Paizo forums. But then, forums in general, especially RPG product ones, tend to attract the worst of the worst. And yeah, the WoTC forums are pretty bad in general.
Truth be told, whatever your reasons are, are just that, your reasons. I personally never had any issues with WoTC, but I had plenty with Paizo. I still bought the PFRPG core book and Ultimate Combat.
As for what they did to the Realms, anything was better than having to do mental circles around the novel canon. Yes, yes, you can ignore the canon, except when the product books that you buy are written with the canon in mind. For hypothetical example, let's say you like the King of Cormyr, but in the novels he's dead. But you never read the novels, and never cared to, so you buy the Cormyr book expecting that he's still alive. But no, he's dead and his daughter is charge. Which immediately changes the dynamic you were planning to go for.
Well, you know the King well enough to wing it. But then you decide to buy the Zhentarim book, which is after that particular incident, and find that everything is written with the Queen in mind, who, if memory serves was quite different than her father. Now, the issue becomes how much effort do you need to do to switch everything back to what you think would happen, or simply suck it and change your campaign. Now, for some of us, that's easy. For others, like me, just simply not that smart to do so.
What's worse is in Elminster's, and his circle of friends' case, they have pretty much done everything! He's got all the spells, he's level 45, CR 39, most of the Seven Sisters are still alive, and being mages or magic users, are also in the high 30 level range. All the possible places to explore, they've already cleared out. And all the magical items you find in there? Well, they all come from Elmy's immense cache of magical toys, every so often he will sneak into 'dungeons' and leave 'gifts' for the adventurers to find. Like some fantasy realm Santa Claus. Yes, kids, the Forgotten Realms is nothing more than an amusement park for your players, because every major threat that pops or popped up, Elmy and Crew (Which includes the not-so-friend Khelben "Blackstaff" Arunsun of Waterdeep, well, if they hadn't killed him for plot reasons, not that anything realmwise would have actually hurt him) can or have already dealt with it!
That's what Ed Greenwood turned it into. By the by, the whole Elminster leaving treasure in dungeons for the 'adventurers' to find and feel speshul was something Mr. Greenwood once mention in an interview. This is what people want to go back to? Where every epic level character had a flavour of arcane magic, or was a full on wizard? Most of the 'high level' non mages never broke 3e's level cap of 20. The highest that I remember was the Drizzle and he was about... 16? 17? 3 Levels of Fighter, 1 of Barbarian, and 12 (or was it 13? I forget, I don't have that book anymore. Damn bed bugs) of Ranger.
So really, turning the Inner Sea into a pool of Shadow (which by the way is pretty damn awesome, when you think about it, more mysteries for players to solve!) and 'blowing up' Thay? You know, Thay is still there, in fact for the last three Encounter seasons, they've been the ultimate badguys in all of it. And right now, we're dealing with a plan of Szass Tam's. Hell, there's apparently a civil war brewing in it, which is kinda realistic, when you have that many folks with arcane power and willingness to use it. So I have no idea what you mean by that (really I don't. Are you upset about their fixation on Necromancy? Which, if I remember rightly, was something that happened at the end of 3e... But I'm not sure. I'd honestly like to know what you mean by that.)
And finally, a World of Darkness, I'm not entirely sure what you mean? Are you talking about the whole 'Points of Light' idea? Where you have small bastions of somewhat civilized lands (Like Neverwinter, Waterdeep, Cormyr, Sembia and other locales) and surrounded by swathes of 'darkness' which are ruins and dungeons and small pockets of evil for your players to explore and deal with? Kind of what D&D has technically always done (which I admit confused me no end when they said the 'Points of Light' was their goal. I mean, that's what D&D has always been about, right? Seriously, how many official pre-3e adventures start off with the players in a local area, like a village or a city, that had some dangerous ruins or encampment nearby that the players had to clear out? That's pretty much what they meant by points of light, so why was it important all of a sudden, when that's the name of the game, since 1974? Whatever.)
Also, I'm pretty sure than any of the settings that Paizo put out is pretty much 'Points of Light' in theme, after all, we're here to adventure and smite 'Evil' in the face! At least I am.