Besides both being MOBA, I think they're just different, and appeal do different people or could be played together other then excluding one another.
Dota and League never appealed to me cause:
-Too long matches (40~60 minutes) for not too much free time to play.
-Items: Besides some people like it to customize their heroes, it deviates my attention cause I don't want to learn wich items to use during the match, making tons of wrong choices and being criticised the entire match.
-Independent experience: Again, for someone starting, just like me, it is a pain to keep up with your experienced team mates... and again, they're gonna blame you the entire match for every mistake it happens.
-Coins: Same as above!
Heroes of the Storm in another hand, allows me to learn while playing, and besides I do need to deal with constant whinners I keep up with the team level, only need to learn about my favorite heroes talents builds, don't need to worry about picking money up and spending it right, and the matches are way faster and batter paced, with 20 minutes of constant action! Also, I really like that "MMORPG" trinity of support, tank and assassin classes, aswell as all of those different objectives each map offers, making every match to feel fresh and recquiring different team oriented strategies!
I'm having much more fun with HotS then I could imagine to have with Dota or LoL, but I can understand that those who likes LoL and Dota and plays for a while may want to keep playing them giving the number of heroes available, the stabilished player base, and the more original style of the old Dota.