Titan was scrapped for a variety of reasons, but I contend that the #1 sole reason Titan never came to be was because Blizzard realized that they are dominant on all genres of games except 1: First Person Shooters.
Although it was widely known that Titan would have been a First Person Shooter MMO, the MMO part was the problem.
Blizzard already has the dominant end all be all MMO in the industry. They already have the end all be all RTS in the industry (Starcraft franchise), they broke into the card game market and now they are the industry leader for that (Hearthstone). They broke into the MOBA market and now they are climbing their way up to being one of the top MOBAs in the industry.
They were no where to be found in the FPS market, and that is a HUGE market.
Titan was scrapped and elements of it were kept and the game was converted into a real team based FPS. I contend that the majority of the players of Overwatch are all completely brand NEW customers to Blizzard.
Sure a Titan MMO would have attracted new players to MMOs, and probably some FPS players, but it would have been too much "cannibalizing" their already acquired customer base. Making the game a pure FPS, they were able to take away a lot of the call of duty gamers and the battlefield gamers.
I believe they still want to create a new MMO, as their mothership MMO (WoW) is aging and they could very well consolidate the MMO market yet again like they did with WoW. Possibly as an mmo in one of their existing franchises (World of Diablo???)
Thoughts?