...is trying to make the character through the game. The voicelines and interactions they have _in the game_ reveal more about Ekko than his lore. People are angry about this because it means he has a small lore section, but if you'd pay attention a little bit you'd know he's a lot deeper than what they wrote in that particular piece of the internet.
There's this thing called direct and indirect characterization. If Riot wrote down in the lore, "Ekko doesn't like Zaunite scientists, they muck stuff up" it'd be direct characterization. They are telling you what Ekko is. But if you are playing Ekko in game, and he says, "You're everything wrong with Zaun!" Then you infer in your mind what he's like. It says no where that he doesn't like Zaun scientists, you just heard him say the above quote.
For some reason it appears that the vast majority of the community would rather be spoon fed exact answers, and don't get me wrong, there isn't anything wrong with that and I don't think any less of anyone who thinks that way. I'm like that with stuff too, sometimes. I like to _know_ that a character acts this way for a certain reason, but most of the time it isn't like that.
I'm pretty surprised you aren't happy that they are using more indirect characterization than before, there is a gold mine's worth of theory-crafting involved in the process of picking apart the champion, and a lot of it is extremely interesting.
And don't comment yet, saying that you're mad because you don't know any specific stories about Ekko and that's why you're complaining. From his teaser, you saw pictures of possibly Vi and Jinx, and then when the mural on his wall was destroyed, he wanted to go back in time to fight the big brutish guy just to fix it. From his dialogue there, I can tell he's a perfectionist in a way, and/or has an emotional tie to whoever is on the mural, and probably has a past with Jinx/Vi.
I got all that because of a few seconds of video, not because Riot told me.