Agreed, and I get your Smash analogy. To clarify: you dont/cant always design for things directly and plan out exactly what kind of gameplay will emerge. A lot of successful games (by many measures) weren't designed from the ground up to cheese the masses and maximize revenues or twitch popularity - they just made it cause the gameplay was fun or novel and it caught on. Current relevant example: agar.io. That game is tremendously popular for something slapped together in a basement on a budget.
Going back to the early days of WoW (i.e. 2005-2006 ish --> beta, vanilla, and maybe s1), it would have been hard to predict pvp-related elements developing into tournaments worth $200,000 USD. To make such a prediction, you'd have to look at the development of the esports scene as a whole, plot the groing trend, and extrapolate: "ok, WoW can probably ride that wave and take a slice of it". WoW pvp in isolation was a joke relative to anything else on the circuits until maybe its golden years (i.e. 2008-2010 --> late tbc to end of wotlk). During that time there was enough hype to actually and legitimately consider it an esport, irregardless of whether it was designed for it or not.
With WoW numbers in decline the esport aspect is going completely niche. Maybe that means, for semantics, you down-rate it from "world popular esport" to "competitive game title". You've still got a lot of tryhard support from Blizz which is to be commended. A lot of other companies would wash their hands of a 10 year old product. But its hard to compare since a lot of other companies haven't charged $15/month to play a game. And since 2011-ish pay-to-play and grind-to-compete have been considered industry no-no's.
I'm glad these WoW/Blizzcon tourneys are still around, and I'm glad Blizz still makes an effort to support the pvp side of its mmorpg pve masterpiece. The game has far exceeded whatever level of esports design WoW originally had. Now factor in 10 years of changing pvp demands, changing esports/spectator expectations, and by 2015 a completely emerged knowledge about the genre and how to compete in it. For all the flak the company gets, it has made some pretty decent efforts to keep up with 10 years of WoW evolution, and evolution of/within the context of esports as a whole.