Mayhaps it has something to do with the dev's who's job was to write the dialogue, are confined specifically to the development of Legends of Runeterra- not the MOBA. So either their time gets consumed pursuing projects that doesn't benefit the Card game. Or the story developers for champions & reworks find time in their busy schedule to pursue something that's not for a new champion, reworks or the extension of lore products for the Universe site.
Plus it's only what, arguable that Vladimir or Katarina could benefit from new VO? But like, majority of the champs who're from both games still have decently serviceable VO with their MOBA counterpart even if the card game has more modernized versions. I don't think examples like Jinx's current dialogue needs any additions.