Jason Schreier's recent book covers some of the game cancellations. The Warcraft adventure game was cancelled after they flew out one of the best designers in the genre for a week to try to make it work, and make it fun, and couldn't. It was a game that was outsourced to a different company, and they didn't feel like it was up to their quality standards to ship. Shutting down Blizzard North came about as a consequence of the distance between them and HQ, leading to a different studio culture that became difficult to manage, and the uncontested resignation of Blizzard North's executive team when they tried to make demands from Blizzard's owners, Vivendi.
Polygon [1] covered the Starcraft: Ghost game. Long story short, it got canned because it was in development hell for too long. Originally under development by a studio in the Bay area, there apparently wasn't a dedicated Blizzard producer to the game for the longest time, and the idea of what it should be kept changing as new games came out and HQ wanted them to copy those ideas. At some point, Blizzard shifted development to a different studio just miles away from them because they wanted multiplayer, but the same issues persisted. And then they released WoW, which consumed all of their attention. With the release of the gen 7 consoles around the corner, requiring further investment, they made the sensible choice to shelve it so they could focus their time and money on their new cash-printing machine instead.
Experimentation is important for finding the fun, and cancelling what isn't working is a required part of the process. And while, yes, there's a ton of games in the Blizzard graveyard, they're no exception. Valve has a list of cancelled games that's probably just as long. And they're all the better for it. Titan died in favor of Overwatch, Nomad died in favor of World of Warcraft.
[1] https://www.polygon.com/2016/7/5/11819438/starcraft-ghost-wh...