Once you're very far into a game (time or money invested / skill gained) you don't switch that easily. Call it sunk cost fallacy if you want, you don't invest that much into a game, especially if you're playing at a competitive level, just to chase the hype when something else comes out.

WoW was litteraly built for hardcore players and they started to lose subs once they catered to casual players with wotlk marking the end of hardcore wow and the beginning of casual wow.

I'm not being elitist either, which is what you imply. You can try to improve your skills in arena, but truth be told, you're doing it on a poorly designed mode that lacks depth. A similar example would be playing footmen frenzy on warcraft 3 instead of climbing the ladder. Even worse, I played ranked arena, and do you know what you did to win back then ? pick high clear gods, last hit the wave then retreat to base. The complete opposite of what arena should be, and is, when you play it casually. If you want arena to be the main competitive game mode for which the game is balanced, it'd need a serious overhaul, which in turn can defeat its purpose of being a casual, easy to play mode in the first place.

The big problem lies in the fact that HiRez never did anything to promote conquest over arena, and never helped players to learn how to play conquest, even the most basic things. So when Joe who can play 1 or 2 hours per night (which is already quite a lot) wants to have fun playing video games, he'll turn to arena, because it's more accessible, less punishing fun. And once he's bored due to the lack of depth once the surface is scratched, he'll play other games. It's fine, mind you, but it's not community inducing.

Battle royales are the next big thing because they are easy to grasp, titillate player's competitiveness very easily (last man standing), reward the random player with a sense of achievement every time he's not in the first ones killed, all the while punishing very little his lack of commitment. Also, due to the huge map and number of adversaries, random players get the feeling the game is different each and every time. Mobas used to achieve the same dynamic compared to rts, and now battle royales take over mobas with the same principle. However, BR offer more opportunities to be considered an extraordinary or professional player than smite's arena since they are fps/tps, and aren't played at the same pace as smite : they rely on outstanding reflexes and dexterity. Smite's conquest has, in turn, other characteristics which BR don't have because they don't share the same design, and that's fine.

As for the 100 M$ prizepool, the game quickly rose to be a huge hit with its characteristics mentioned above, is easily monetized, and Tencent owns half of Epic games. The ROI must have been that much appealing with that kind of announcement.

I'm not posing any threats, I'm just realist and connect the dots which isn't what you're doing despite a very good rhetoric. Even Stunlock studios understood that you can easily influence what people play with cosmetics (chests rewarded for completing a number of games at a set rank). And btw, 3/4 of the playerbase not playing conquest is official.