The idea is noble. But the thing is, the game is designed and patterned to collectible cards. It really isnt a big hit in my country, but every now and then, some of these collectible cards, from marvel characters to Pokémon to baseball cards to basketball players, etc., these cards are bought in packs of 10 (I think most of them do), but the contents therein, the cards themselves, are unknown. Most of the time, you get dupes or multiples of the same card, and in a very small odds, you get the rare, and at the very very very dismal odds, you get the rarest among the rares. I think that may be the reason why the heroes are also on a card. You need to summon for them. You need to collect them.
Otherwise, there’s no fun if everyone got all the heroes. It would boring too quick. That may be the reason of the allure of those collectibles, Pokémon go, and the rest of them.