I feel like Blizzard is just putting out a MOBA with popular characters and expecting it to become an e-sport whereas to break into the scene now takes alot. SMITE is a good example. HiRez (the company why makes SMITE) have put their all behind the game and it's taken quite alot of work for it to get to where it is now. The Twitch viewer numbers and player base is nowhere near that or LoL or Dota2 however they have managed to achieve massive like events with large prize pools (this upcoming world tournament is over 1.5million dollars in prize money), they are also partnered with Tencent and have a Chinese release.
Blizzard is doing little to push HotS right now and the lengthy exclusive alpha and beta periods will not help this. One thing that has been made plainly clear is that people lose interest fast in a game they cannot access as has been shown by games such as Strife, Dawngate, Infinite Crisis, and the other MOBA attempts that are really going nowhere. SMITE also has gone for a third person over the shoulder skill shot based gameplay rather than the traditional RTS style camera and click based play, this allows it to find it's own market as well. HotS is simply too close to LoL and Dota2 and the lack of a standardised competition map will also hinder it. Another thing learned in the e-sports scene is that limitations in the playing field are better than too much variety. This is why SC2 struggles at times as the map pool begins to influence the results more than players in some situations.
Blizzard has not shown it is capable of really handling e-sports properly either. The showcasing at Blizzcon shows this as they are treated as secondary events happening alongside other stuff rather than as a true showcased event.
Hearthstone however is seated in a unique niche right now as it is the best example of an online only CCG and has a reasonable level of complexity. It is also reasonably fast paced so can function on a spectator level.
HotS has about as much e-sport potential as ARAM matches in LoL do. Don't get me wrong the game is fun, but it's certainly better as a casual game than trying to shoehorn it into true e-sport status.