I left playing PokemonGo after playiing for over 2 years in favor of this game not by reason of the “gonna catch them all” slogan, but because of the constant walking and running around the town needed for a player to progress. As far as I know, E&P does not have that PokokenGo’s slogan. Only moneyed players and heavy spenders try to get all the available heroes they can . I know there are several players who have all the legendary ninja heroes but may be lacking several event or seasonal heroes, or HOTMs. I refuse to believe that a player has all the heroes, except if you are part of SGG staff trying the heroes in the live game. Otherwise, that would be insane.
As mentioned by posters above, new heroes keep this game going. I really think they will be introducing more
legendary heroes in the existing challenge and seasonal events as some only has 3 or 4 of them in it. They may also introduce a new monthly challenge event after the success of Wonderland. Besides, season 4 may have been already in the development.
Imagine if there were no new heroes, we are stuck with S1, S2 and S3 legendaries. No HOTMs. No challenge or seasonal heroes. This game could have already died years ago.